Since the only difference (from what I've read) between 2.5 & 2.6 is the elimination of a magnetometer (compass) from the 2.6 board, you may find that a 2.5 version that allows you to disable that chip, which some have found to be flakey in mutli-rotor use, would save money, while allowing you to buy the same combo GPS & mag you would have bought for the 2.6 anyway.
HobbyKing sells a 2.5 kit (from their international warehouse) with a combo GPS/mag. Then you probably want the telemetry transmitter/receiver too.