Who wants a friendly feral?!

My neuter date with the ASPCA isn't until June 12th, and I don't want Miss Mama to get preggers again--I'd like to get her spayed ASAP. I borrowed a trap from a co-worker who does this sort of thing all the time, so that's not an issue--I just need to figure out where to get her fixed. I really can't afford to pay $40 out of pocket for it, it would be really crazy cat lady of me to be fiscally irresponsible like that. It would be different if someone wanted her...
She and the kids seemed to enjoy the 3/$1 "sardine cat food" (it was a can packed with nothing but aspic and lots of real smelly sardines! yummers!) I put out. They had a nice family dinner together except for the one baby who was more interested in this little hole he was digging than in the meal.