Hi Josh,
most of the good US Turbochips go for over $20 on ebay but you can find good deals if you keep checking. The fact that you're willing to take games without boxs and manuals will help you keep the costs down.
Keep your eyes out for small lots of turbochips on ebay.
as far as websites go,
www.tzd.com still has a few US hucards, all brand new.
www.estarland.com sells used games for reasonable prices.
Darkman (
http://www.darkcityproductions.com/duo/index.shtml) got his site back up and a good, somewhat outdated, list of online vendors can be found there. some of the links are broken for vendors that are still around so try to google the vendor if a link doesn't work.
it's easier to find PC Engine hucards for cheap prices, but remember that you can't play them without a converter or a modified system. not-too-good converters usually go for $50+ on ebay and a new, high quality converter can be had for $100 at TZD but it sounds like that's out of your range.
if you go to
www.pcecp.com you can search for a list of all of the hucards released in the US and check out screen shots.
there are tons of good games i'd like to recommend, but i'm only going to list some that are usually fairly cheap.
*Bloody Wolf
*Bonk 1+2
*Alien Crush (Devil's Crush is a little better but a lot more expensive.)
*Dragon's Curse (part of the Wonderboy/Adventure Island series)
*Dungeon Explorer (not really an RPG, more of a fast paced Gauntlet-style game, also multi-player)
*Legendary Axe 1+2
*JJ and Jeff
*Motoroader
*Raiden
heck, pick up Keith Courage if you don't already have it. that should be the cheapest game out there and it's a pretty solid platformer