What do you plan on using it for?
If you're using it just to play music through your computer to larger theater speakers, you can get a basic amplifier/receiver on craigslist or even ebay for about $40 (max), unless you want a super fantsy one. But the fact that some computer audio programs have an equilizer and other sound modification programs you really don't need a super fantsy one. If you're in no hurry you can probably get a pretty good deal on one.