Makerbots are a fairly reliable commercial kit, easy to put together and good print quality.
RepRap printers are open source 3D printers, you can get this as a kit, though it's possible to build them yourself if you have access to a 3d printer already so you can print the components. It uses other bits of open source technology like Arduino boards, and driver software. My housemate built one this year, easier to build than I would have expected, though you'd have to be reasonably technically minded and quite patient.
If you're not keen to build or buy a 3D printer then there's companies online like Shapeways that will take a digital file, print your object and post it out to you. They print in umpteen different materials, including metal (not cheap)
I've though about using the printer to make caving related stuff myself, but I can't see a huge amount of applications beyond small clips and the like.