I usually feed baby retics sub-adult mice. And as the snake grows graduate up to larger and larger food items. From mice, to rats, to rabbits, etc. I only feed pre-killed prey items. I never feed live. With live prey you risk harm to the snake from being bitten by the prey. I buy enough frozen mice/rats at one time to last me a month or two. That way I can thaw out enough for one feeding and leave the rest frozen until the next feeding. Some keepers also buy live prey and kill it before offering it to the snake. You still eliminate the chance of your snake being bitten, and the prey is still fresh this way. But whenever possible I stick to the frozen/thawed method, it's easier and much more convenient.
I feed baby retics one mouse every 6 or 7 days, and large retics I feed an appropriate sized prey item every 7 to 10 days. Not everyone will agree with that schedule, some keepers feed more often and some wait longer between feedings. That method just seems to work for me.
As far as the price goes, if you buy your frozen mice from a pet store you'll usually be paying more then if you were to purchase online, say from rodentpro.com. Usually when you buy online there is a minimum ammount you can order, but you save alot of money in the long run. I would check both online and at local pet stores in your area to give you an idea of how much it's going to cost to feed a retic. Remember an adult retic will be able to eat a large rabbit very easily.
Mike