metal gasket and cleaning out engine on 2003 Pontiac Montana

The mechanic has told me that the intake gasket needs replacing and the engine cleaned out because coolant has gotten mixed in. He also recommended a metal gasket, because the old one was plastic and that a plastic one will eventually fail again and I will have the same problem again. I understand the need for metal over a platic one, but is cleaning the engine out necessary and should it cost $1,000 or more as he told me it might.

Asked by for the 2003 Pontiac Montana
gm has an updated intake set that will not leak as the old ones did. i would not vary from gm gasket.
flushing the engine is a must as coolant in the oil will destroy the bearings.
the price is a little high but in the ball park. we are at 985 plus any accessories it may need.

Thanks, I thought I might be getting ripped but I'm not. It seems my mechanic is being honest. Sad for my pocket book though.