Lump on Archie

I was feeling Archie's leg Yesterday, because he's got mats in his fur. I found a strange feeling one, and I found that it's actually his skin. It's near the base of his tail, on the back of his leg, and it feels like a mat. It's skin, though. It's firm, and not soft like the fatty tumors I find on my dogs. It's not attached to muscle or anything... I don't know how long it's been there. I never really feel back there... Archie is 10 years old, by the way.

Archie is my foster dog, he's not my own. That doesn't really make a difference, because I'll pay for whatever he needs. But I know that if I ask the vet, they'll probably say "Well, watch it, and see if it gets any bigger." That's what they always say with my dogs.

Now, I don't want to adopt Archie out, just to have someone receive a dog with a malignant tumor or anything. Do you think a biopsy is a good thing to have done? Does anybody know the general cost of a biopsy?

And just for good measure--

Hello,
From what I have read biopsies can cost between 50-150 dollars (it depends on the vet and whether or not you decide on removal). I think that it would be worthwhile, so that you could know what kind of cells are in the mass. It's really great that you found it, regardless of how long it has been there, because now you can make sure it isn't anything more serious. I think that if I was the one adopting him, I would just want you to tell me that this is something that you are concerned about and looking into. He seems like an amazing dog, and I can't think of any reason why the right forever home for him wouldn't love him regardless. Best of luck.