1998 Boxster camshaft adjustor solenoids -- help!

[98BoxsterNY]

Greetings! Recently my 1998 Boxster has shown "check engine" codes -- sometimes P1531 and other times P1530, which my mechanic says are caused by faulty camshaft adjuster solenoids. He said the codes indicated that both solenoids were bad, but was hesitant to do the job because the solenoids are roughly $900/each, and he could not guarantee that the problem isn't caused by something else -- like a bad seal or something.

The mechanic (whom I trust) said that the car could be driven regardless, however I have read that this could cause engine failure. Does anyone have any advice on (1) what could be causing these engine codes, (2) places where I could find less expensive parts, or (3) whether continuing to drive could harm the engine? I don't really have $2,000 to get the job done, unfortunately.

THANKS!! -- Jon