Anything below that price range is most likely going to be junk status (unless it’s something on sale, or a clearance of old stock)
In your first post you said light workout. Depending on what you do, it CAN be a light workout. But in most disciplines, and especially while learning, you will get tired very quickly, as anyone learning does. Unicycling uses a lot of strange muscle groups that most people are not used to, and when learning, you don’t know how to conserve energy through proper speed regulation. Also you are falling and getting back on a lot, which uses a lot of energy as well.
Point is, don’t get discouraged at first if you find it hard to practice for even a few minutes. Make sure to wear protective gear, an injury while learning can really put people off and discourage them from riding.
Good luck! Always remember, you’re not balancing on top of the unicycle, you’re just regulating the speed of the wheel so it stays under you!