If feeder price is a concern in the long run, I'd recommend buying in bulk rather than individually at pet stores. Far better priced and more consistent sizes and quality. Perfect Prey and Big cheese rodent factory are the popular choices, however big cheese tends to run out of their small rats super fast!

I just got my first order from Perfect Prey. Including shipping for 40 feeder items, I paid $65, which should last me for approximately 8 months for one snake. (Give or take depending how many may be refused/wasted) so that comes down to less than $10 a month. Keep in mind prices vary according to prey size, but hopefully this gives you an idea of price range.

You may want to consider a mini freezer if your parents are not thrilled to have dead mice/rats stocked in their freezer with their other food lol