cheap/easy way to swap valve springs at home

Two types of valve spring compressors. Overhead type and the larger "c" shaped lever type. Lever type is costly-best to rent, faster, but have to have heads off. The overhead type can be used with heads on. Definitely have to break the keepers loose by smacking with a socket and hammer to bounce the spring, many times they come out. Some sort of stand or blocks of wood help. If heads are on the motor, an air hold fitting keeps the valves up. I've used my quick detach compression tester hose hooked to an air hose and compressor to do the job.