yo, bacarolle, imma gonna let you in a little secret.

You say you're in Boston (me too), so, look up Simple Living Cycles (its in Frammingham) and head on over there to buy yourself a Redline 925 or other actual name brand fixed-gear that fits your budget. Word of advice, make sure everything on the bike is tight (lockring, cog, everything, especially lockring/cog). If you don't know how, take it to someone who does.

Either do this ^, or order something from BikesDirect (but you'll still run into the whole problem of making sure your bike is set up properly).