The $149 Mongoose is not actually a fixed gear, but what WalMart calls a "fixed speed" bike... which I think is a made-up term smooshing together "single speed" and "fixed gear" into a true knock-off.
I called our local WalMart to see if one could acquire a fixed speed in Portland. Alas, the clerk on hand reported there were none in the store. Though it took a while to track down the right clerk because it turns out that WalMart keeps bikes in the "toys" section.
Though I couldn't snag a bike, BikeSnob got a Mongoose online (before they were backordered) and has a characteristically devastating review.