air pumps?

[cobalt]

On a recent trip to Albuquerque with the 2006 Forrester XT, My check engine light came on. The dealer said it was a bad secondary air pump related to emissions control. He replaced it for about 600.00 ouch! 2 days later the check engine light came on again. Dealer says bad primary air pump. This only cost 400.00 because it`s easier to get to. He says it`s caused by cheap gas and short trips without the engine getting warmed up.

Has anyone heard or experienced this ? I did check with my home town Subaru dealer and he quoted the same prices for the service.