Wow. That is an expensive monthly cost.
For a 6 tub rat colony, it cost me $30 a month to maintain them. But I sell some of the babies to pay for that cost, so the rats are paying for their own upkeep aside from my own time and effort.
I think i your situation, it will be cheaper to breed.
It will cost you less than what I pay since you only have 3 snakes. A 50 pound bag of food lasts me a month. With the same bag of food, it lasted my friend with mice a couple months. 50 pound bag of mazuri costs me $27. Kiln dried pine bedding cost $6, but lasts me two months.