2005 Ford Explorer Thermastat Housing

My daughter drives this vehicle. Teenager. The engine overheated a month ago and I put in 1 gallon of antifreeze and some water. Watched closely for a week all was ok. Then my daughter called to say it overheated. Went to look and I could smell anti-freeze but there was smoke coming from around the manifold. Radiator and overflow container had antifreeze overflow down about 4 inches. Took into Firestone and they pressure tested. Looks like there is a leak in the Thermostat Housing. They also did not rule out the plastic manifold over the engine. Looks like Thermostat housing is OEM and prices out at around $139. This includes top and bottom plus gaskets and replacement thermostat. How difficult is this to do myself? I have a minor mechanic ability. Total cost with labor and flush is $500+. What do you recommend?