How much should it cost to replace a head gasket?

Please look here for head gasket replacement estimates: https://repairpal.com/estimator/nissan/altima

its not cheap

Prices vary from state to state. Most repair facilities (and manuals) include an unnecessary removal of the under-carriage...and quote a 10-11 hour labor charge. The actual job is about 71/2 hours and shoild run about $900, parts and labor.