Low Cost DACs


Currently I have my laptop connected directly via 1/8 jack from headphone outlet into 2 RCAs directly into my tube amp. Quality of sound is lacking to say the least!
I am considering adding an inexpensive DAC ( iFi AUDIO nano iDSD LE Portable DAC  or iFi Audio nano iOne DAC ) into the stream between the laptop & amp.My question is: will this influence the overall sound I'll hear out of my speakers? Will adding such a DAC help to increase the quality of sound produced by the system?
I'm not interested in spending a lot of money on a DAC as this is a source that I don't use as much as some others already in the system.
wcc10
I just bought a used Micromega MyDac for $110 and was very impressed.  There are a lot better DACs out there but it was a nice intro. 
The thought process / flow is correct for improvement.
USB / Coax would be a preference.
Note that differences (at the PC) in "Sound" will be heard from one brand to another.
Mac difference once again.
I think you’ll be better off, sound quality wise and may be even cost wise, if you just get a dedicated streamer/DAC instead of inserting something between your laptop and amplifier. The usual recommendation is a Bluesound Node2i at around $500 or a Node2 at a lower price.
Thanks for the input.I am currently streaming via an OPPO BDP Blu-ray/Streamer.I have a Pandora account and unfortunately with the OPPO you can not save or play specific albums or individual songs, only can save different genre "stations." To save albums/songs to a playlist you need a computer. (go figure) So this is why I want to get better sound via the laptop. and yes, $500.00 is more than I want to spend on this. I'm looking at a ceiling of $200.00.
Might try a Topping D50 about $250 new it uses the latest 9038 sabre chip and is one of the best measuring DAC's. Might find one $200 or less used.