I purchased a home (9 yrs ago) where the previous owner had the sprinkler system's control valves buried in the ground with 'plastic' covers. The man who does repairs on the system came to check on zone 1 and in doing so said zone 3 selenoid wire broke off and he had to replace it - charged $25 +. Is this normal? Is there any other solution other than replacement?

Sounds reasonable to me. Most of the solenoid coils have leads that are part of the coil, if it breaks off at the coil, there is no repair, must replace it.