People who are building fun things to ride on during events: do you have any tips on where to get started?

After seeing people have tons of fun with home built vehicles at #gpn20 I really want to make my own.

I already have a rough design planned out but I'm wondering where I could source the parts cheaply.
I've seen lots of vehicles built from these "hoverboard" things but those still seem a bit expensive, at least on eBay.