My 01 blazer with 4.3 has a blown head gasket I believe. 110500 miles it overheated and now oil end up in radiator and coolant disappears. How expensive is this to fix and should I just but a low mileage used engine to replace it.

Blown head gaskets are not a common problem with this engine however, lower intake manifold gaskets are a very well known problem. Either gasket can leak coolant internally and/or externally. Oil does not pass through the intake gaskets. There are oil passages in the head gasket but it's rare for them to leak oil into the coolant. A more common way for oil to enter the coolant is from a leaking oil cooler inside the radiator.

The OEM intake gaskets use a plastic cage with a molded silicone rubber insert. If it's not leaking now, it will, guaranteed, they all do. Felpro makes a replacement gasket set that uses a steel cage and a rubber seal... they don't leak, (if installed correctly). Part number is: MS98002T and is available at most auto parts stores. Hope this helps.

Coolant disappears and it appears oil is in radiator brand new radiator so I believe head gasket is the problem