Pixie&Truffles

Just to confirm it is mast cell even though she's almost certain

Hi guys, I'm new here.. I took my border collie to the vet on Thursday after a lump came up on her head on Monday, I thought she must have just bumped her head when playing so wasn't too worried. Off to the vet on Thursday we went because it hadn't changed, they took a FNA and they are almost certain it is a mast cell tumour, I have never dealt with a dog with cancer before, my fist dog is 14 years old and still in great health so I guess I always thought she would get ill before the younger one... Anyway, Truffles is going in for surgery to get the lump removed on Friday and the vet has recommended getting the biopsy sent away to confirm, this costs an extra $300 which being a full time student is hard to afford, I was thinking it might be better to save that money and put it towards any further surgeries she may need. What would you do? The vet is already pretty certain it's mast cell, so do you think saving the money and putting it towards further surgeries is a good idea? So confused and looking for advice