

So I suppose I should start from the beginning, shouldn't I?
So a few months ago (maybe five or six) I noticed a small lump, about the size of a pea, on my cavy's side. I was a little panicked, because she's one of the first guinea pigs I've ever had and I had never experienced something like this before.
So we took her to the vet that week, and she told us that there were a lot of possibilities of what it could be (cyst, tumor, fatty lipoma, etc.), but she wouldn't be able to tell us exactly what it was unless we ran some tests and sent it to the lab for a biopsy.
Now, to book an appointment at our local vet costs about $80 just for her to take a look at it and give her opinion. She ran some numbers for us and gave us an estimated sum of what it would cost to send it to the lab. It came to about $800.
Since it wasn't that big, and it didn't seem to be bothering her, we decided to wait and see before making a decision.
Now, fastforward six months, and this is what it's grown into. It's about the size of a cotton ball now, and I can almost move it around, if that makes sense. As much as I would love to take her to the vet and have this monstrosity removed, we just don't have that kind of money. We could easily walk in, pay the $80 for the vet to have a look, but I know exactly what she would recommend; do the biopsy. There is a huge difference between 80 and 800.
She's about three years old, and hasn't had any health problems before. She hasn't stopped eating, drinking, or pooping, and while she has lost some weight it's not a substantial amount. I would just like to know if anyone (someone with more experience with this than I have) can identify what this is and let me know what my options are? I would appreciate any input.