Maybe you live in an apartment or you live with family who isn’t understanding about the hobby. That’s okay, you can still learn a lot about engines, mechanics, and restoration techniques for a lot less money and a smaller footprint.
Some of the big advantages of a moped are they’re cheap, in many places they don’t require a license, and they might actually be really useful around town or campus. The engines are ridiculously easy to rebuild and they usually have enough bodywork to get some paint experience as well. Lastly, there’s a strong enough market for classic mopeds that you might be able to make your money back as well.
Old Lawn Tractors
Most people wouldn’t call these fun or exciting. But with modern lawn equipment being built cheaper and cheaper, an older tractor could serve you for decades. In the US, many old tractors have very durable Briggs and Stratton engines that still have good parts availability. The older ones often have quite nice styling if you’re into that kind of thing. Look for Wheel Horse, Gravely, Cub Cadet, and even old Kubotas. If you live with parents this might be an easy sell with the folks as well!
This one is a bit tricky if you don’t have a motorcycle enjoyment and they’re more complex than their little cousin, the moped. They are small though and older Japanese bikes can be had for just a few hundred. Take a scroll through Bike EXIF and inspiration might strike.
Just a motor
This one isn’t for everyone. Most motor rebuilds will cost some money and an amateur should be prepared for a steep learning curve. It’s probably best to have someone experienced to help you through it and field questions. This probably makes the most sense if you’re space limited but not money limited, doing a proper motor build can cost money. However, if you already know what kind of car or motor you want to have you’re going to have to spend that money anyway.