Go visit your local Velodrome - there may be bikes for sale. My track had some nice used track-ready bikes at very attractive prices ($500 to $1000) last year.
Also bikes I would trust can be bought from Dolan
Dolan Bikes - Track Bikes
Prices shown include UK VAT not charged to US customers, but shipping would be extra. The US dollar is currently strong against the UK pound.
There is a 54" Specialized bike here for $330. Probably a good intro bike that would keep its value on resale; it would need a larger chain ring.
http://stores.ebay.com/The-Pros-Clos...34Q2ec0Q2em322
[Pros-Closet is a reliable and also a sponsor of my local Velodrome.]