Remember a great way of raising funds is to try and sell things on Ebay!
Might sound a bit silly, but I've sold loads of stuff like old Cd's bits and pieces that were of no use to me anymore. It all adds up.
You may have old books lying around you don't want anymore, it could be anything really. Have a think about it, it could come off.
Best of luck with getting these cats fixed, the sooner the better as in kitten season they can get pregnant virtually straight away as you know.