brake problem...PLEASE HELP!!!

i have a 99 GMC SONOMA with the 4.3. my brakes went out today on the way to work...pedal to the floor and nothing happened. i managed to get around the corner and get stopped. i got it home with no problems, but i have no idea whats wrong with it. the guy at a shop around here said proportioning valve, ABS shit, or master cylinder. does this sound right. anyone know what it might cost to fix it?

he also said that if its the ABS shit, itll be expensive, but cant u just bypass all of that? is that reliable?

Any good suggestions would help???

I had a 96 s-10 body dropped with the abs taken off i never had any problems with it. and now i have a 2000 sonoma and the e-brake and abs light have been on for a while now im thinkin about doing the same thing to this one too