I have to agree the prices are high but that is the nature of retail petshops. Things need to be marked up to make money. A freezer is not cheap to run so they have to mark up to contribute to the rest of the overheads of the store.
I personally can't breed rats where I am but I find no problems with buying rats in bulk and storing them in a dedicated freezer (which the bulk discounts paid for) and I also keep a number of other peoples in there and sell packs to people who need it for a marked up price. This price covers freight and starts paying back some of the costs and if others buy me out I just place another order.. we are not talking 50 rats we are talking 100's which I understand others can't afford straight up but if you can get a few people together its worth it!!
Word of Warning: get the money for them BEFORE you order if others are going in with you.. If they don't pick them up then its not your problem!!