Had to put down a kitten because of financial issues

On the 26th, a stray gave birth on our porch. We brought her and her babies in. Today, one of them had such a horribly swollen leg that we took him to the vet. The vet said that they didn't really know what caused it either and that the kitten was too young for anesthesia so they could amputate him. He said that it'd be very expensive to get him treated and even then he might not make it. 1k immediately and then more later. My mom couldn't afford all that so the vet said that putting him down was the most humane option.

It feels bad. He shouldn't have to die because of money but he did.