Like Miss Vicky said, prices will always vary with vets. One vet wanted to charge me $300+ for removing a tumor from a boy I had several years ago. I actually just had one of my older lady rats Gypsy (almost 2 yrs old) have a small tumor removed yesterday. They labeled it as a minor lumpectomy and said it would range from $110-$130. I wound up being charged $110, which I think is a reasonable price. With the documents I received upon pickup, they listed all of the things that I was charged for, which was really just the supplies used during her procedure - anesthesia, minor pain medication after surgery for when she woke up, etc. This is also just the surgery, though -- this doesn't include the biopsy if you chose to do that.
If you do want to help your friend, I would just look for vets in the area that care for rats or "exotic animals." An appointment at the vet just for checkup shouldn't be too much (my vet charges me around $20-$25 per appointment but again, all offices are different), but you or your friend will need to call around. After the vet looks over the tumor or mass, they should be able to let you know the approximate price range that they'll be charging you. You're not obligated to schedule the surgery.