You are skirting the used category budget wise. If that's OK with you, go ahead and look around in your city for a reputable used audio shop. That's where the best bargains are on the good quality stuff. AVSforum.com will tell you more about what to focus on. Too much to write up here that isn't already covered over there in greater detail.

**Keep in mind if you are mostly focused on music and not surround sound for movies, spending a much higher portion of your budget on the speakers should be considered. Do *not* buy any Bose equipment, btw.

All that said, you can go 2.1 now and buy new at the entry level for price/quality. Amazon sells a basic entry level Polk Audio T50 speaker for $99. (I still prefer to look around for a gently used high quality speaker, but this would get you there faster.) Two of those and an Onkyo/Denon/Marantz/Sony/reputable brand 5.1 receiver with all the bells/whistles can be had for <=$300. At that price point the quality of the mass produced receivers is very similar IME and O. Only the slight differences in features or personal preference for brand might sway you purchase one over another. (Hint: Ask yourself if you need future expansion capabilities such as 7.1 or 5.2/ATMOS, etc. Might you need bluetooth or iPod connectivity, etc.?)