A guy at work has a 200cc Lifan Chinese enduro- he paid about $1,300 for it new. He had to go through some extra paperwork to get the registration and title for it- I don’t think you can legally ride them on public roads in California, because of the clean air laws, even though it was mailed partly assembled from a warehouse in California to Kentucky.
He has rode his for 4 years with no problems- it had some extra valve noise and needed the valve clearances adjusted, but this is part of the normal maintenance. It has enough power for 55mph roads but not for faster roads. The light weight and low power makes it better for a beginner, and the insurance premiums are low.
Instead of rebuilding the engine, you can just bolt in a new one: