for anyone who has seen my two other threads, i'm considering adding a subwoofer to my planned system. i'm putting together just a simple budget system to listen to music in my room (home and college). i'm not sure which receiver will be used. the speakers are Energy C-200's.

so i'm considering adding a subwoofer to the equation. so far what i've found to have good reviews in my price range are:
Sony SA-W2500
Polk Audio PSW10
Infinity PS28
Evidence MKII

do any of you have experience with these, or opinions on others?

as you can see, i'm putting my budget at about $200. also, in this range, would i be better off buying new or used?

thanks.