First, I agree with everyone who had the point of what are you breeding towards? Most people in my area will not pay what a rabbit should go for to ensure more than a neglectful home, and so selling is tough around my location. Even more so for mutts than pure bred rabbits. I had several people 'kindly' offer me $10 (1/4 of what I was asking...) for my good quality show Champagne d'Argents when I was breeding them, and they acted like that was even too much. Needless to say I didn't bother to reply to their emails. It would be best to have a specific goal in mind to breed towards and a plan for the extra kits you can't sell (unless you intend to eat them, and then that takes care of that).
Second, if you are breeding for meat, I would like to ad that if your not crossing with a high production breed or lines, I would personally stay away from Rex. It could easily just be the rabbits in my area, but all my Rex and crosses thereof have grown extremely slow, from 2 different lines I tried, so I gave up on that breed in a hurry. I have had really good luck crossing Champagne d'Argent and French Angoras and getting some monster kits (5# by 9 weeks) with two different lines of each breed, but I may have just gotten lucky there.