Do you know how to neuter a male cat yourself? The ones around the barn are getting expensive to bring in to the vet for the procedure. It seems like it might be a simple enough process if there's a way to immobilize the cat.
Please do not try to do this yourself! Look around your community and surrounding towns for places that offer low-cost spay/neuter services. If you don't have a clinic near you that offers discounted services, talk to your vet about a discount. Some vets will discount services for feral/community cats.
Why not just find other ways to save money...do you do your own dentistry? Perhaps just have going to craigslist for a prostate exam, or just maybe DONT OWN AN ANIMAL IF YOU CANT PROVIDE BASIC HEALTHCARE FOR IT.
Its not like there are not a plethora of low cost animal shelter options out there in most any area. Call the local shelter/ASPCA - talking around $10-15 a cat here and there are places that will waive this with income verification.
Bottom line, dont practice surgery if your not a surgeon. Theres a reason they go to school and not a 4 hour training seminar on how to neuter an animal.