I just ask people for a voluntary donation to help the next needy guinea pig, usually £10 ish. The only thing that matters though is the home
................ if people are generous too that's a bonus.
I've rehomed over 100 cats and dogs myself and I could count on one hand the people who have been "very very generous" but as long as the home is perfect for the animal little else matters. I know that that particular animal will always have what it needs but often people don't understand the concept of rescue's financial burdens and needs, there is that feeling that they are doing enough just by offering a good home. Sadly it isn't always enough but very welcome none the less.
When a rehoming has gone particularly well and the people are genuinely overjoyed with their new arrival that sometimes has to be reward enough and it does encourage us to keep going.