Yea i personally am a big fan of the 'broke student 5.1 Surround Special'
Using a 4 Channel Car-fi amp(4x100W typical) ~$25-$50 used, usually powered by a PC ATX PSU or similar (practically free as in beer).
A 5.1 USB soundcard($20ish) hardwired directly to amp + Guitar/Bass amplifier($50) used as subwoofer.
Decent speakers bought used can be had for around $50 a pair, good speakers last for decades unlike most crap made nowadays, so just spend whatever you can reasonably afford, since it's a fair investment in the long run, just make sure to check they still work(no damaged tweeter/woofer units).
Use standard Cat-5 network cable for signal cable AND speaker cable(double up), failing that regular mains cable works too, again free as in beer.
Use media player/OS driver to mix center channel into front speakers.
Bonus points for:
Soldering the connections.
6 ch. car amp, bridge one pair for center speaker, or get a powered full range PA mono speaker(easily found used).
Braiding the Cat-5 cables, with honors if the speakers you got can be bi-amped and the braid uses it(2 bass and one for treble/tweeters)
Using a studio grade soundcard, firewire ones tend to be common, useful if you have the connector anyway.
If you can find a mains power noise filter and/or have proper ground connections.
Using the guitar amp for it's intended purpose.
Optional mounting hardware.
I've had people compare such setups to $10K+ supposedly high-end gear, they can be amazingly high fidelity
for what can be done on a very frugal budget.
Don't get frightened by how it looks, just consider it 'ART' =)