If you are buying for the track, get a track geometry. The Langster is a really nice bike, but is a road geometry because it is designed for comfortable road use. That $100 CL bike you found is a conversion and I don't think would even be allowed on the track. I don't know if the Langster would be allowed either.
You have a really odd selection. The only track bike you picked out is the Bikes Direct (Mercier Kilo TT) which is a great bike for the money. $350 is excellent price, or you can get the pro, which has better components and a brake (put on for street, take off for the track).
Other options would be a Bianchi Pista or a Fuji Track. They are the usual default low cost option track bikes.