I got kind of lucky here because my company grew out of the failure of my old employer. They basically ran out of money and sold themselves to a very large company. That company didn't want a subset of the users, so we offered to purchase them. I just used the same pricing scheme as my old employer did to make the transition for the old users as palatable as possible to increase the amount of people that stayed on through the migration from my old company to my new company. It worked fairly well as close to 80% stayed on.