I finally purchased a cat/raccoon-sized Havahart trap yesterday, and I've set it out and baited it! There are four known targets--two ferals, two abandoned. At least one of the abandoned cats is clearly unneutered; the status of the ferals is unknown. I really really really wish I could get the two abandoned cats into no-kill shelters, but everywhere I've called is full.
Biggest thing for me now is--patience. My summer schedule is slower, so this is the perfect time to trap, but I don't have forever. It's raining tonight, and trapping tends to be slower then. Oh, and we have a resident raccoon and possum, and they're bound to set the thing off occasionally.
Despite these minor obstacles, actually getting the procedure won't be a major financial problem: There's a low-cost clinic in town that will do the whole procedure for less than $50, including a rabies shot. However, I have to get 'em in before 9 in the morning. For this and a few other reasons, I'm only going to have the trap set during the early and late evening hours.
Wish me luck!