From B&S, we have:

Crank: 167.25
Rod: 31.40
Pin: 5.60
Piston: 73.20 std, 78.40 +.020
Gasket Set: 56.80

With the +.020 piston, that comes to 339.45. I don't know for sure that it needs a piston or pin, but chances are good that the piston should be replaced and the pin is cheap. That's a lot of scratch for an old lawn mower engine.

I found on www.smallenginesuppliers.com an engine with a different part number, but otherwise looks identical, for $450 plus shipping. Comes with everything but the exhaust. That might be a better way to go, unless it's possible to find a used crank.