How much is a head gasket for a 2011 Hyundai Sonata?

Is it worth fixing a blown head gasket?

A vehicle's head gasket is worth fixing, so long as the vehicle was in good condition prior to head gasket failure. To help calculate if it's worth fixing, follow this 3 step process: Determine the resale value of your vehicle if repaired. Get repair cost estimates.

Is it cheaper to replace a head gasket or replace engine?

Changing the engine generally will cost a ton more money than simply replacing the head gasket. So, unless your cylinder head is damaged beyond repair, and you won't know that without stripping the cylinder head. Replacing the gasket is the most cost effective route.