Its difficult to level just one fret. If you don't touch the ones on either side, how do you know when you are down to true level? Any small, flat surface a few inches long will help a lot. Even wood, though it may not stay flat for long. Stick some 320 grit paper to it (use rubber cement if you don't want to buy a roll of sticky sandpaper). Mark all your fret tops with a dark felt tip pen, then sand the fret tops until every fret has a sanding mark. If only miniscule amounts have been removed you can just polish and play, no need to crown. If your frets were really wacked out you should have the proper tools to make things right. Not to mention the proper experience. I'm not sure why uke people will attempt repair work that guitar players wouldn't think of trying. Perhaps they are more adventurous. Or maybe its just because their instruments are typically a lot cheaper. I encourage people to learn this stuff, but having a pro rescue your botched frets may cost you more in the long run.
Sorry for the long answer. The short answer is, what are your ukes worth to you? Tools seem expensive, but they last a long time.