Because I don't want to derail this thread and have it turn into a mega-rat thread, I'll direct you
here and
here. Although in my experience keeping them has been relatively cheap. I've always made their food by buying the most healthy ingredients in bulk and mixing it myself in large quantities. You can build their enclosure, which should be large, or order one from
this manufacturer, which is who I [and my friends] have used with great success. I personally like the R-695 model.
EDIT: Although you should never take on the responsibility of any pet thinking it's going to be a 'cheap' relationship. A few months back Dorian and I had to spend roughly three hundred dollars on emergency vet bills for our rabbit who, until that point, was costing us about twenty dollars every two months. It's generally a good idea to have an emergency fund set aside for
any animal you keep, because emergencies
do happen.