a check up might be your best bet, but you might want to try to talk to a vet if you cant visit one. just try to strike  up a q&a session.

It is under the skin, and kind of moves around 

The lump is about the size of a nickel. I have a vet appointment in a couple of hours, I'm hoping it isn't anything serious.

I have only had the girls about a month now, after adopting them from the human society. I did not notice anything on her then. It does seem to have just popped up. I'll know after I talk to the vet  She is still a happy, active ratty 

Its one of the classic places for a mammary tumour.  How old is this sweetie supposed to be approximately?

Don't worry, it is better to have tumors removed right away, but she wont be hurt by waiting. When Fizzgig got her first tumor, my vet at the time told me it didn't need to be removed. I finally had enough of this thing because she couldn't even walk anymore. She got through surgery just fine with our new vet even though that thing was over half her weight. She just went through another tumor removal at 33 months and is doing wonderfully. Just get rid of it as soon as you can! Good luck!

maybe he does it on a case by case situation.....in anycase he's still a jerk

Not having it removed right away won't hurt her. Some mammary tumours grow slowly as well too.
Save up for that surgery and she'll be just fine. 

It sucks not being able to pay in payments, so I've had to get a care credit card. Every single vet I've been to in the area requires payment when services are rendered. (Not to thread jack)- My rottie (she's deaf) was freaking at our fence because a large dog was trying to jump the fence. My parents male minpin (she grew up with him and our chihauha scottie mix)was trying to protect her, but missed jumping at the fence and jumped on her back. I guess she thought she was being attacked from behind, and turned and grabbed him by the neck. A hole in his esophogus and windpipe, almost died in the car, and the vet insisted after he was stabilized but before surgery, I better find a way to pay or they'd have to stop treatment. Care credit is the ONLY thing that has allowed me to keep my pets.

I guess I can understand that why they want payment up front, but if you're a consistent patient, I'm not sure why they can't work around it. It just sucks. Hopefully your girl will be all set with you continuing to do the great job you're doing until you can afford it. Good luck to you and  and  to your girl!