New Head Gasket Needed - Cost is $1800. Does this sound possible? on 2000 Nissan Altima

My son needed the head gasket replaced on his Nissan and the cost was estimated at $1200 until the mechanic got inside and discovered he needed a valve job. This cost another $550. Is this possible. We trying to come up with the money, for we believed we didn't have a choice.

Asked by for the 2000 Nissan Altima
Shop around, but it's probably to late. Sounds a little high but what can you do now.