Yo I’m on the hunt for a cheap highway legal bike that responds well to hypermiling. I need it for practical reasons: being poor, needing to occasionally carry a lot of stuff long distance.
I’m really aiming to get 90mpg around a city but I understand if that’s basically impossible.
Good luck in your search, but I'm afraid anything that can get 90 MPG city isn't going to be able to reasonably keep up at highway speeds, and probably isn't going to be able to carry much luggage either.
Usually Dual Purpose bikes like the Suzuki DR650SE get great fuel mileage and they are relatively low maintenance compared to other bikes. Suzuki has been making this same bike since the 90s. Any scooter or dual purpose bike that has a 300cc engine or bigger should be good for highway speeds. Scooters tend to be a bit more expensive.
I agree, it's hard for a bike to get 100mpg and be cheap as well. Here is an article from 2023 on the most fuel efficient bikes. I remember reading this a while back.