If you only have the one snake I wouldn't even consider it. Even with a single male and female, you're going to be spending much more time on your rat husbandry than with your snakes. You're also looking at annoying rat maintenance bills (rat food is oddly expensive if you don't buy bulk) and the hassle around having to euthanize them to prevent them outgrowing your snake. Basically you're going to be paying the same as buying bulk f/t but with a lot more work and weird smells.