That really, really sucks-- it seems like we have a neverending caravan to the vet's office, so I know how you feel. I think the last 2 week period alone has cost me about $500 (NOT including the usual pills, supplements and shots).
Some idiot's loose collie mix tried to attack Robin; our poor girl slipped her collar, too, and took off running down the street. Luckily my husband intervened before it got bad. I'd take them to small claims court. Sometimes it's not worth the hassle, but vet bills rack up...and quickly, as you know.
When Robin was spayed, she had a baseball sized lump; the internal stiches were rubbing an irritation. The vet did an aspiration to make sure it was just fluid, and we kept her on a round of antiobiotics and warm compresses. It finally reabsorbed.
Good luck-- thinking good thoughts for your crew.
"In these bodies, we will live; in these bodies we will die.
Where you invest your love, you invest your life." --Marcus Mumford