Not as cheap depending on your definition perhaps for $500 on the used market are the all copper braid trio, an entry level cable from Jena labs. These are just very high quality copper in a typical braid that happen to sound fantastic in my system.
Used Cardas would also be on my list for Merlin but not the Neutral whatevers you want the Golden whatevers but for $500 you should consider the Cross whatevers. The Cardas copper in those cables is excellent.
An off the wall pick ....that I have used on a couple of occassions... that simply sound good even though they are cheap are the Pheonix Gold Bulk cable! Get them in a fairly heavy guage. I use the ones, that are blue and white spiraled a somewhat big wire which my dealer custom terminated for me as I required (small spades one side Banannas on the other in a biwire) very low cost well under your $500 limit for an 8' pair. I got them from Agon dealer "Quest For Sound." You will loose Cache but of course not the sound of good thick copper which the Merlins seem to love.
At first don't be surprised that you are not blown away by them but leave them in your system for a good while. I did that and did a "shoot out" with some very fancy cables and these came out on top. Not just my ears of course. I did eventually let the upgrade bug hit and used Jena cables. However I still use these in a second type system.
