I’m a high school student who wants to build an electric motorcycle as my senior project and i want the cheapest build while maintaining high quality. (as you can tell from my question, I’m not very experienced at this)

I’m not sure, but I think 72 volt will be more efficient. David N is correct, that a golf cart would be great for parts. But for a motorcycle, you’re probably going to need Lithium Ion batteries (to fit enough on), which are very dangerous, and can cause fires from shorting out. If you want it to actually go above 20mph, you’re probably going to need a stronger motor.