I wouldn't breed mice for 2 snakes to save on 'cost'. Properly setting up the mice, bedding, food, supplies and maintenance will outweigh the cost to purchase live mice from the pet store. Have you tried switching them over to F/T? If so you could order in bulk to save some money.

Breeding rodents can be a very rewarding though, I currently have a small colony of rats.... We have a love/hate relationship =)