It is very possible that you qualify for S/N for free due to limited income issues & you just might be able to receive food for them, also.

Please try contacting the following:

http://www.neuterspay.org/cgi-bin/webdata_pro.pl
http://www.alleycat.org/contact.html
http://www.lovethatcat.com/spayneuter.html

Please keep in mind that the situation you are describing will not get better without spaying & neutering.