Cat very sick green pus severe pain can't eat

This poor cat, that I've named Charlie, is an unowned cat in desperate need of emergency vet care. It has massive amounts of green pus oozing out of its mouth and it is unable to eat. It will die a slow horrible painful death by starvation. It is one of a colony that I have been feeding and is spayed or neutered. I don't know it's sex or age. Please help me. I see this poor cat every night and it's heartbreaking. If the vet recommends euthanizing then that's what will happen. But to allow it to suffer is innhumane.

If it's treatable, then I will treat it. I just can't afford vet bills on top of the $150 a month I'm already spending to feed and care for the colony. Please help, any amount is better than nothing. Thank you

https://photos.app.goo.gl/C56t6nzGDSPL3wLN7