wow, I'm so sorry! that's horrible news about Kara... it seems like you barely just got her
don't give up yet, though - it's not a lost cause!
you might try calling shelters/rabbit rescues to see if they can recommend any cheaper options or any programs that might help fund things for you. I also recommend googling the phrase "help funding vet bills" - I see a number of potentially helpful options in the search results. she could have a few years left if she survived the surgery and the vet was able to get the cancer completely and there ARE programs out there that can assist with medical bills for pets (particularly life-or-death situations like cancer) when their owner is suffering from financial hardships.