blendingnoise,
go with what feels right. that being said , have you looked at the bianchi bergama(sp). it's not a single speed but it's not a bad bike. it might be a bit heavy for what you're looking for. it's also more of a commuter bike. the 04's are selling for 430. you should be able to find a nice single speed for your price range. keep looking. ebay is always another option. there's plenty of single and 3 speeds in your price range. yellowjersey.com has those old raleigh single speeds that are made in india. pretty hot looking bikes. also broadway bikes in boston has a single speed bike that uses a vintage english frame and is built with new components. not sure if they ship. that bike falls in your price range. it all depends on what you're looking for. those bikes might not be the case. there's also folding bikes. redline makes a single speed mountain bike that sells for under 500 new. good luck with your search and school.