TinkerCAD costs $19 per month for the Personal edition and $100/month for the Startup edition. I'd buy a basic CAD package rather than "rent" one month to month. Three-dimensional printers might appeal to more people at a lower cost, but as the cost goes down I expect more small companies to offer 3-D printing services--perhaps even the UPS Store or local Kinkos-Fedex store could make my prototypes.
I no longer make my own printed-circuit boards because I can get a 2-day turnaround from local shops that welcome small orders. And some PCB quick-turn companies also provide the schematic-capture and board-layout tools for free. Watch the same thing happen with 3-D printing.