Rainsoft Q2 timer conversion

I have a Rainsoft Q2 valve water softner system. Purchased in 1992. Over the years we have had to have the piston assy. & sheer pin replaced (usually 1-2 years), last time replace 7/2012 (need one again). Also the motor as well has been replaced. They are recommending to go with a new timer conversion for the system. What should this conversion cost? Recommended due to parts available & old technology.