Checkout about 3d modelling programmes first, unless you have a source of pre defined G-Code output to build the object. If you get over that hurdle, then think about the device where, the more you ay the better it is.
I vaguely know an engineer who has one and who designs and prints his own stuff - I'm aware of replacement knobs for a car parcel shelf and something to do with car door handles.
From the little I know, I'm not sure you'd want to get into designing your own stuff. I believe he ends up doing quite a few prototypes, and he understands what he's doing (and is a very smart engineer).