Welcome to the forum! For cheap and easy, the two quickest routes are probably a charcoal furnace and lost foam casting. Both involve a minimum of equipment and expertise, and a good scrounger can do both dirt cheap. It all depends on what you are trying to do, if you are just making ingots or you have a contract with NASA for space shuttle spare parts

. The best advice I can give you to start out is find your crucible first and build the furnace to suit, and don't get hung up on making it perfect. Aluminum and pot metal are easy to melt, and it doesn't take much of a setup to have good results. Not as specific advice as you would probably want, but I hope it helps. Good luck, think safety first, and post pics of your progress.