Our breed rescue asks for a donation if the new owner wants to give something, and most people give around £100 but we don't turn down a good home if they are unable to give much. If the dogs are elderly we don't ask for a donation, but most still give us something. There are lots of costs involved in rehoming dogs, mostly vet bills, but also transport if the dog has to be moved, kennelling, food, insurance, advertising etc. If you can't afford a big lay out consider an ex racing greyhound, many trainers would have one available free to good homes (although the official retired greyhound trust branches ask for a donation), but you would need to take out insurance in case of vets bills. You can pay monthly for insurance.