Contact Alley Cat Allies http://www.alleycat.org/resources_ancare.html#2 they have many resources on how to start a TNR program, places to contact, etc.

We've been TNRing for over 7 years now. We lucked out, after making numerous phone calls, finding an organization that helps people to trap, get low cost vet prices, etc. It can be costly and once you TNR you need to make sure they have a source of food and water daily. We also provide this for our colonies! Good luck and I commend you for doing this!

Also here's a number to call to find out low cost spay and neutering closest to your area:

1-800-248-7729