unless you are running stuff out commercially I really can't see any reason for you to have to buy prman, one of it's main advantages is it's scalability and extensability and if you have no experience in it, it will seem like the most daunting thing in the world. Large studios use it because it allows them to control their rib(what actually gets rendered) generation, shader assignments, shader descriptions etc etc. For one person sitting at home messing around you definatley dont need prman.
Interestingly though you can now get prman for maya
It's a standalone license and doesnt use alfred etc. I think it's about $1000 but dont quote me on that. That would be a great way to get to learn renderman(which is a great skill if you are looking for a job!)
Technical Director - Framestore
Currently working on: Your Highness