That's a question only you can answer. If you don't mind the smell, and the work, and being tied to you rodents everyday, then go for it. I wouldn't do it just for the money though. Keep in mind that a bag of lab block is $30 bucks and bedding is $6 a bag.

You could always start out with a pregnant mouse for now. At least that way you could feed off the babies if you can't find a market for them.