Get a free bike from your friends/relatives/clients and convert it.
Cheap!
I added some stuff to mine afterwards though - got me a new saddle (now having my eye on one of the Brooks saddles actually), chain and couple of things like shorter chain ring bolts and helmet
Now spending a bit more - just ordered a wheelset. Old one isn't too pretty plus rims are different kind.
Going to have my bike match this pic:
http://tbn0.google.com/images?q=tbn:...ky-T-shirt.jpg