I am fortunate to live in an area (Atlanta, GA) where I have access to some really big names in pool. I got to talk to Johnny Archer. At one point I think it's fair to say he was one of the best nine ball player on the planet. After talking to him a bit I decided not to take lessons from him, and talked to Shawn Putnam since they are both in the same pool hall in the Atlanta area. I talked to Shawn Putnam and he basically told me I would have to unlearn EVERYTHING I know about pool (which is not much) for him to be able to work with me. I did not get the sense that I would have much room for error. I either learned his system or nothing at all. In the end I ended up working with Tim 'The Monk' Miller and the combination of working with him in person and his training material has helped me blossom as a player.
I say all of that to make a few points. As others have suggested and stated, paying more does not always relate to a better experience. A big name does not always translate to a better experience either. I mean one on one lessons from Johnny Archer how could I go wrong? But again, based on a conversation with him I don't think his lessons would have worked for me. Talk to several instructors and get a feel of how well you guys will work together. Also keep in mind how far you want to take your game. No price is a bargain if the lessons do not work for you. Working with someone you enjoy working with might be worth the old brown bag lunch a few extra times a week. Or you might get fortunate and find someone you enjoy working with, is able to help you grow as a player, and is also really affordable to work with.
As far as the measles ball, my understanding (and I leave plenty of room for correction as I do not claim to be an expert) is that ball is lighter than other cue balls (like your black, blue, or red dot cue ball). If you are not using a complete set made specifically for the measles ball you might actually be doing more harm than good to your game. The measles ball is not going to play off other object balls the same way it plays off balls made in sets for the lighter measles ball. Besides, one does not look at the football when throwing it. One does not look at the basketball when shooting it. One does not look at a bowling ball when rolling it. Why would you be looking at the cue ball when shooting? your focus should be your object ball not the cue ball. I am not a fan of something that will train you to take your focus off of the object ball. However, if you are going to train with a measles ball (and I think that is a good idea. One runs across them quite a bit in tournaments since a good number of tournaments use Aramith sets) train with, and get, the whole set and not just the measles ball.
