Here is last year's set of transmissions - the ones this year are almost identical but have a slightly slower low gear and slightly faster high gear. They cost about $130 from start to finish, and they have worked flawlessly for us. They also are not too difficult to put together - one of our engineers explained it to me in about 10 minutes and even now I remember how to put them together.
The ball-lock shifter is done with a 3/4" bore 1/2" stroke pneumatic cylinder. We also have encoders on the shifter that allow us to know when the robot is in high or low gear and deliver that information to an LED on the OI. This year our programmers perfected autoshift when a certain RPM is reached (can't remember what off the top of my head).
Neither the tranny nor the shifter has ever broken (though once we left the pneumatics open and were stuck in low gear for an entire match). They are light, efficient, and small compared to many other transmissions, thus explaining why we continue to use them this year and probably next (unless we are underwater!)