Lump on cat’s thigh

Tonight I discovered what feels like a moderately sized lump on my cats’ (Elsie) thigh. It’s size is about that of a thimble, protruding a few centimeters. I’m obviously pretty concerned, but I’m not sure if it’s the placement of where her microchip is.

The unfortunate aspect of this scenario includes some cost constraints. I recently graduated from college and don’t have the financial means of going through some extreme measures to find out what is wrong— to help in hopefully cutting corners, what are some questions that I should ask? She was adopted from the Humane Society, should I check with them before asking her regular vet? Costs in general, what would a biopsy cost?

Ahh, very nervous for my poor Elsie.