My bunny has a large lump on the middle of her belly?

I recently rehomed a Giant Flemish Rabbit from Craigslist- the owner made her sound too good to be true of course, but I'm concerned about the large lump in the middle of her belly- it looks to me like her urethra but the previous owner said it was just a deformed bellybutton. It's about the size of a lime, and has milky fluid on the end. I don't have a lot of money for expensive veterinary procedures, but I also don't want my new bunny to be in pain or die. Has anyone else had experience with this?