I got a rain sensor at Ace Hardware for $6 and installed it myself - easy to do.

Rain sensor for irrigation
 

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You have received a LOT of replies, but none have answered your original question as to a recommendation for an installer. So to answer your question, you might contact CHAD'S LAWN CARE (352-787-8303). They have a service rep who works on sprinkler systems and think he might be able to install a sensor for you.

I had to replace mine, and they put in a remote sensor that didn't need wires. But that was when I was using Service Smart, and we all know that wasn't a "smart" idea. But Chad's has been very reliable and I've grown to trust their service reps.

Mine was just replaced by ACI Irrigation for $165 as part of an irrigation system wellness visit.

I agree. We had two sensors fail in a relatively short period of time and now just put the system on bypass. As part time residents it is one less thing to worry about when we can't be at our Villages home. Overwatering doesn't seem to do any significant damage the lawn, but underwarering certainly will. Our cost to irrigate the lawn is very low compared to the cost of replacing the sensor multiple times and more importantly it is very low compared to the cost and aggravation of replacing a dead lawn.