Yeah, I've been toying with the same things. Personally, anything bigger than an e-bike gets more difficult. There are a lot of e-bike solutions that will offer decent runtimes/distance and allows you to pedal to increase it a bit.
With larger vehicles, you get into runtime and weight issues, and the sheer amount of battery power they need. As you get heavier, you need higher voltage to deliver the power required, but this requires a LOT of batteries, which makes things heavier. Not to mention the rapidly increasing pricetag of something larger.
Then you have to consider your local, state, and federal laws regarding custom vehicles. There are restrictions in speed, size, style, safety, etc you have to know.
An e-bike is probably the most economical way to go and should stay within fed/state/local laws. But TBH, using R/C electronics is probably more expensive than an off-the-shelf solution.
Here is a site where you can get a 1000w (36-48v) BL motor/ESC combo for $350. Then, you also need ways to mount everything, and some type of throttle control, which that site most likely has.