Interplanetary vehicles are still purpose built and expensive. It is also generally a lot harder to get to another planet than you would expect. As for our own

Interplanetary vehicles are still purpose built and expensive. It is also generally a lot harder to get to another planet than you would expect. As for our own moon, it has an irregular distribution of mass, so nothing that orbits it stays up for very long. Read about PFS-2 if you are interested. I'd imagine that dream isn't too far away though, since orbiters are needed before a manned or most unmanned missions can be sent to a body. NASA's MRO still cost us 700m though, and only 90m of that was related to the launch.