Neutering costs for cats

We have been saving stray cats for over 10 years, we rehomed around 30+ cats. We currently have alot of female cats needed to be neutered and vaccinated before rehoming. The monthly medical costs + food are around 300$ so there isnt much money left to pay neutering for 7 female cats we have along with special food after for the recovering. We do not get any kind of money support from our country and everything is paid out of our pockets. We currently have 13 cats in our care that need to be rehomed.