Need to raise money to spay two stray cats that keep having kittens!

There is two stray mothers who are continuously producing litters outside of a nice mans house who is feeding them He has put the kittens up for adoption. However i would like to nip it in the bud, instead of finding the kittens homes, lets get the females spayed!! The two females both had a litter 3 months ago, the kittens are now up for adoption. Although one of the females is already pregnant again! and the other one probably will be soon aswell.