1994 Pontiac Bonneville Power steering goes off & on

At slow speed recently, the dash lights lit up, there was a "bing" alarm sound, and the power steering quit, causing my son to pull off to the shoulder. He turned off the car and then turned it back on. When it came back on, the power steering seemed to work fine. He drove directly to a gas station and checked the engine. The fluid in the Power Steering reservoir was at a good level, The hoses are okay and so is the fan belt. I took it to our dealer and a new guy I don't know called me the next day and said the belt, pulley and reservoir are okay, but that a hose that leads to the rack & pinion has a small leak. He says the problem is a valve inside the rack & pinion needs to be replaced, and that it might shut down any time. To repair it they want over $1,100.
It all sounds okay to me except for the price. Are they accurate or trying to rip me off?