I have a ban Colt M4 with a muzzel brake and fixed stock. I want to put a FH and real colapsable stock on it. I would like to stay with Colt parts. Who does this and about how much should I expect to pay?

www.Adcofirearms.com and www.ar15barrels.com, as well as others, can remove your brake (if present) and thread your barrel.  If it needs to be permanently installed (as in the case of a 14.5" barrel), they can do that, too.  I advise letting people who are used to doing this do this operation for you.  

As far as the bayonet lug... why bother?  It is very difficult to install a whole new front sight base to fit the previous pin holes.  Leave well enough alone and skip the bayo lug is my advise.

You can install a new CAR or M4 buttstock assembly yourself, you can find instructions here, I think they are tacked.