I would recommend f/t for sure.
Make sure that you do not buy too many. You can't keep them in the freezer forever. Lots of people recommend 6 months I think. I have heard they might be fine up to a year though? Maybe someone could back me up.
What size are the rats you were looking at for 5-8 bucks? Where I live, rats are illegal period. They do not exist period, and have to be shipped in! You can probably guess we pay BANK for rats.