I know you are not going to like reading this and I hope you do not see this as an attack. If you can not afford the proper food and you can not afford proper bedding, why are you buying more rats or raising rats at all? I think a better option is to switch your snakes over to F/T and give up the rats.
If you can not afford to feed f/t, then maybe you can not afford to keep snakes yet. It may be a good idea to wait until your finances and living conditions are in a little better shape before spending disposable income on this hobby.