Regular replacement of drive belts on Lawnrake?

I have a Performance Power Lawn Rake 600w PWR600LRC. Unfortunately the drive belt on the side of the Rake keeps coming off the spindle, often braking without hardly any use having been made. Regularly replacing the belt is rather expensive. Have any modifications been made to the Rake to stop this occuring (e.g. a different spindle with a lip on it to stop the belt coming off, changes to drive spindle to enable different tensions to be made to the drive belt etc? Has this problem been raised on many occasions? What is the current price for replacement belts?