Basic 12g copper speaker cables to $$$ cables.

How much do you have to spend to hear a difference? In other words, is an $80 upgrade worth bothering with? $200? $800? Etc. Let's say we're talking about an 8K system, with speakers as the best component.
Hi Thomas the whole thing matter but other thing need to be in order like speaker placement room treatment carpet, etc.  if you have quality component and the above you will see a different. If you have one speaker in a corner and the other out in the wide open with tv above and big dirty window behind you head, save the money or spend on weights or something g to get your body big and strong and turn woman head like me.

I was in this exact same situation, very recently. My overall 2 channel system is right in the ballpark in that overall cost, a bit more but close, (most purchased used). My last emphasis has been upgrading cables, starting with the IC’s, and speaker cables next.I had been running some 10awg basic ‘pure copper’ (yea, right) cables in bi-wire configuration to my Vandersteen’s. They sounded fine, but knew I could do better, and it was time.

My rig is off to the side, and if left that way, I would have needed two 15-16’ bi-wire cables. That length can get expensive given some of the upgrade choices. Shorter speaker cable lengths are preferred anyway, provide many more options, (especially on the used market), and would also reduce cost. Thus, first I made decision to move my old Belles amp to the floor between the Vandy’s. But, that decision made a longer IC from my pre to Belles amp necessary ($$).

First, I didn’t want to spend the cost of my overall rig on speaker cables. After much thought, study, reading options on various manufacturer options, I finally set my sight on NOS Western Electric tinned copper cable. From what I had read, they just sounded ‘right’ *for me*. Found a gentleman who has 1950’s NOS Western Electric 10awg cable, and could custom make an 8’ bi-wire set for me. Luckily, he also gave me a couple options for a 10’ length of IC I now needed, also made with NOS Western Electric wire, (not the same as the speaker wire).

My overall cost was about $440 less tax and shipping. But, that included a 10’ IC cable. If we call the IC $150ish, let’s say my speaker cables cost $300. Is there a difference? Absolutely, in a positive way. Am I pleased? Yes I am. Not only about the sound improvement, but also because I ‘think’ I have cables more ‘in-line’ with the rest of my system, and I ‘think’ it was an overall good investment.

Could I have spent less? Yes, much less on other speaker cable options, but may not have gotten a significant difference over my ‘basic’ 10awg cable. As example, I looked at Canare via Blue Jean for $150. But, I will never know for sure what the actual difference might have been between those and the NOS Western Electric cables I purchased, or even over my old basic copper cables. Or, more expensive Kimber on the used market for that matter. Sometimes these are decisions we have to make a bit ‘blind’, factoring in many different things. #1 being a desire for change. What is right for one person may not be for another. I could have left what I had alone as well. I could have, but most of here on this forum won’t.

But, to your question, it’s pretty hard to identify a certain $X amount of dollars that will improve your system over what you have currently. Only you can decide that.
It's a reasonable question, but IMO it's impossible to answer.  It all depends on system synergy and your taste.  I have two different sets of speakers.  With one speaker - same room and system, I prefer my $100 Belden cables to a set of $1500 cables from another company.  With the other speaker, the Beldens are impossible to listen to and the more expensive cables are worth every cent in the amount of improvement they render. I think it's always a good idea to start with ordinary decent copper cables to get a baseline.  You should list your system and the members here may be able to give you some good recommendations.  You should also try to state what you are trying to achieve as an upgrade and they type of music you listen to.  I know - you listen to "everything".  Everybody but me does too. So maybe just what you listen to the most will suffice.  
Thanks for the help. What I know about cables could fit into A thimble, at least as far as actual experience goes Like everyone else, I can read about them online. 
OP it has NEVER been about dollar amount. It is about the construct used and how they were put together. There is NO SUPER duper change because of price.. There is however a correlation between a good business model that gives you more each time you pay more.

Me I jump to the position I like in sound, and have for quite some time. Speaker and gear type, really don’t change for me.. Just like the rooms I use.. The cables I build would be tough to better for what they do.. I don’t care who makes the cables... I have had some serious cables over here for 2 to three weeks at a time to be fair off and on for 4-5 years now.. It is tough to beat some of the weaves, and helical builds, with just a little effort and a few good parts.. YES some are pretty spendy. ALL under 500.00 usd, No matter what I do.. Pure silver $$$$

I’ve built cables for 45 years for HEAVY equipment.. this stuff is pretty easy to figure out.. It’s A Cable for God sakes.. Not made by cable gods.. just stiffs like me... with good parts.. I’m a happy fellow..

If was gonna spend money on cables, I use the business model I posted. The more you pay the more you get...That is what most of us want anyway.. RIGHT?

So here’s what I have. Maybe someone could offer specific low, mid, and high budget good matches. I know even less about interconnect cables, so I’m open to hearing about the difference they can make and what someone might recommend as well. I have a musical fidelity a308 amp going into ATCSCM 40 V2s. It’s a very complex, difficult room, with no options to change that part of the equation.Any ideas?
I’ve been all the over the spectrum with cables, including a $14,000 loom of Nordost Frey 2 with the QX4 and QB8 etc. In my opinion cables are the last 10 percent that can really increase your connection to the music. They don’t need to cost as much as a car, but if someone tells you they don’t matter, get advise elsewhere.
The first indication of a cable change for me comes from background listening over the day. Little things that get your attention, or not. Give them time don’t just cycle through them like socks.
I’d say $8k system, start with $1k if you can. If you can get a set priced right you might be out $50 if you resell. Maybe you are satisfied maybe not, but that's what I would suggest.  More money doesn't always mean better, but it typically does IMO.
Find a store, any store, that has speaker cables, power cords, or interconnects they will let you either demo in store or take home and try. Does not really matter at this point if you listen to speaker cables, interconnects, or power cords. They all make a difference. The question you are trying to answer, how much for YOU to hear a difference. Only you can answer this question, and you can only answer by trying. 

Me personally, a very long time ago, I did this and the difference between my freebie wire and the one the store had was night and day, and that was "only" a $175 interconnect. But- and this is a very important BUT!- you may not hear any difference at all. Or it may be that in your system a cable upgrade is not appropriate anyway. Like if your speaker cables have to go 20 feet, one is ten, must hide behind furniture, etc. In that case you will be smarter to go with interconnects and power cords that will give you the same improvement, but without the hassle and expense of speaker cables.

First though you must answer your question by actually going and listening and finding out for yourself.