Had a plumber come out and give an estimate of $739.00 to install a check valve and hose bib assembly for a feed to my sprinkler system. Is this on the high end?
You do NOT need a check valve and a backflow valve. You need either a pressure vacuum breaker, or a reduced pressure backflow preventer. The more expensive reduced pressure valve COULD cost 740 installed, but not likely in the system you have.