You can do this on your own, you know. I did. Start with course grit sandpapaer and get finer and finer, ending with 1000, 2000, 4000, and finally imperial lapping film by 3m. Hold the sandpaper in your hand and run it up and down the length of the shaft ALL THE WHILE TURNING THE SHAFT WITH THE OTHER HAND...apply pressure evenly and past the ferrule. If you don't run it past the ferrule you'll get a concave arc in the shaft nearer to the ferrule. Cover the joint with tape so it doesn't get scratched.
Always change the motion constantly so that the sanding is evenly done - if you use only one sanding motion, the shaft will be uneven from doing it the same way continually. It sounds scary but it's not. I've done 3 shafts that way with 2k cues.