Light bike, fat bastard, heavy bike, slim(er) bastard?

Agreed. Splash out every penny you have (and as many that you don't have as the bank will let you) on a fine steed.
The pleasure you will derive from riding it will far outweigh the gloom created by hunger and balifs.
Just don't let it get nicked.

cheap bikes from legit brands ride well! In any event - don't ride the mountain bike. Life is too short and that... If you want to ride the fancy bikes just get insurance...