I’ve got some standing orders of 1 or 2 euros every month for bigger projects like grapheneos and kde. And for small apps that I actively use, I try to donate 5 or 10 euros now and then. It’s not much but I believe if everyone is doing their part we succeed in the long run
Depends on the project and the kind of utility I get from it. Up to $20 USD typically, but I’ve donated more for specific cases.