How much should a person spend to get a decent power conditioner?

Please help me understand what you mean by 'Power Conditioner'?

There are units with surge suppression and filtration to reduce noise and harmonics on the line.  Then there are units which re-generate the AC voltage. This it the type I use and have noticed quite an improvement in the sonic ability of my system over the filtration/surge suppressor type I had previously.  I do recommend this type.

New or used?  I purchased my PS Audio P5 used and paid about $700 for it.  Well worth it.  It did have a flaw in the display which is common.  But it does not affect the units performance and reliability.  In fact, for the most part the display is off.  

I have had several PS Audio  units. They are well built and have had a positive impact on the sound as long as i did not try to run a amp thought them. The last one a P10 i still have, but no longer use. I now use High Fidelity MC 6 Hemisphere half the price and a much richer and detailed sound than what i got with the P10. The Hemisphere is for front end equipment only ( no amps). I gave up surge and spike protection, but the sound was much better with the Hemisphere.
Good luck
Pete

Well the ideal of perfectly designed components, cables, and reliable clean power is mostly a pipe dream....

to wit I bet you will find many a dirty wall watt switching supply in many many systems

most people have at minimum a network switch nearby and the wall wart to power it.

most servers, DACA, etc lack a properly designed Faraday cage to keep the analog side clean...

so gathering all your dirty dirty stuff up into a low end $500 Furman or similar and putting that on a dedicated circuit will do wonders for your and most any system

i have all three of my systems wired this way, two w Furman, one Isotek

In my experience, probably 2g is my cap

the right one does make an audible difference

Btw
bought both Furman for less than $250....each
they are out there....