2000 Dodge van 3.9 blown head gasket??

How much would it cost to repair a blown head gasket???
They advertise a blown head gasket sealer on the internet for $100.
Does anyone know if this works????

Forget the sealer, that's only good for the one trip down to trade the vehicle in for a new one.

DIY: $100
Shop: $600 (give or take)