Bike Buggy How Hard Would It Be To Build A Cheap Little Motorized Buggy/bike For Under $200?

How hard would it be to build a cheap little motorized buggy/bike for under $200? - bike buggy

So I thought it would be great, could have a small car for a few horsepower. I understand that this does not go to the park and probably me one years, but somehow he can not help me begin to learn to build things with an engine / motor could help. As someone has had experience with it?

PS: I probably would have a welder and other things that I have some tools.