Yes it takes extra time. You still have to draw up the part etc so there is no savings there. The materials aren't all the expensive from what I remember. The expense is the initial purchase of the device.

Rapid prototyping machines come in various forms and some are cheaper than others. It depends on what your needs are as to how extensive or costly you need.

I do love the finished products. If I were doing it for my own model and it wasn't a pert I could reproduce with out great difficulty I'd draw the part in 3D cadd and shop for someone to make it on the net. Lots cheaper that way.