The cost to have a crankshaft turned or machined by a machine shop or engine rebuilding shop can vary.
I've seen prices from $45.00 to $50.00 to have a crankshaft turned or machined and I've seen some shops charge as much as $100.00 to $150.00 for the crankshaft to be turned and machined to be repaired.
The machine shop or engine rebuild shop will place the crankshaft on the lathe and then grind it smooth and check for the correct tolerances etc.
Usually when you have spun rod bearings then the spun rod bearings will do some damage to the crankshaft which then either needs to be repaired or replaced.
The grinder will grind the crankshaft smooth and then you may need some smaller or larger bearings to match up with the machined or turned crankshaft.
Sometimes you can buy a new crankshaft for what it costs to have the old crankshaft turned but if you can have the crankshaft turned for $100.00 or less then it's usually worth it.