Normally I'd be right there with you on the Best Buy part but I've ordered a few things from this site and had excellent experiences every time. The prices are very low and the products arrived in perfect condition. Only one product didn't have the original box, the other boxes had some wear and tear but the components themselves all looked and performed like brand new. On top of that the customer service of a large company can't be beat. One of the amps I bought was missing a set screw for the power wire, I called BB to see if they had any extra they could send me. They were going to RMA the amp and send me a whole new one! I said nevemind I'll check the hardware store but good to know they don't mess around. Turns out the setscrew was loose in the box, must have rattled out during shipping. If op needs a DVC 4ohm sub then yes maybe he can stick with his friends sub, which could also have been thrashed though. He did say what ohm he needs or what amp if he has one yet. Just trying to throw out some price conscious suggestions out there. There is also this guy
RE Audio SRI10 10" Dual 2 ohm 300W SRi Car Subwoofer, a few people on this site have picked one up, I haven't tried mine yet but the specs look good and is a step up in power from the Polk without going crazy.