1997 Taoyato Camry misfiring; blown head gasket?

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Just purchased a used 1997 Toyota Camry, 161K miles. Ran fine for a month but then statred misfiring. After tuneup (plugs, wires and new valve cover gasket) the engine is still misfiring on two cylinders (code verified). New mechanic says it is a blown head gasket and wants 750 for gasket repair and replacement of timing belt and water pump. Does this sound reasonable? Any suggestions?