Nissan Pathfinder head gasket

Is it worth repairing a 2002-04 Nissan Pathfinder head gasket? What should the approximate cost be

That will depend on what condition the rest of the vehicle is in and the cost will vary greatly based on the type of shop and the locale.

An even bigger factor are the circumstances leading up to this head gasket failure. If the gasket just let go suddenly for no obvious reason then it could be a cut and dried repair.
If this vehicle severely overheated or had a history of overheating it’s possible that you could have an oil burning engine after the repair because excessive heat can fry valve seals and even worse, piston rings and cylinder walls.

Coolant diluted engine oil can wash out crankshaft bearings and cam lobes. This scenario or the severe overheating one could mean a shaky engine at best even after a head gasket repair.