They tend to be quite big and a bit more expensive, but inexpensive Onkyo amp are still remarkably good.

I ended up with a low end Onkyo TX-NR for my home PC. Ii takes 5.1 audio input via HDMI, and it sounds great. And it has all the benefits of a good amp.

Interestingly, I later decided to connect my home server video output to it, and I ended up using it as a HDMI switcher. But that was not the initial intent and even without such additional benefit it was still worth its cost.

I remember I spent around € 200 on it back then, but I can't remember the exact model now (I'll check once at home).

However, it was a predecessor to this, which I believe costs cost less than $300.
http://www.uk.onkyo.com/en/products/tx-nr414-75913.html