With a small collection of snakes, it's really not practical to breed your own rodents...unless you just really love the little critters and can get as much enjoyment out of keeping them as you do your own snakes.
If I were in your shoes, I'd opt for buying frozen online. You may not even need a separate freezer. Unless you're buying tons of them, they don't take up that much space in a regular freezer...especially as you're not going for jumbo rats or anything.