I doubt changing the prices had anything to do with Gallagher's exit. More likely, they were entering their final few weeks of performances, realized demand might be higher for tickets, and saw an opportunity to make a little more money. Wouldn't be the first time rush prices were raised near the end of the run.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body