Sinclair neck turner with 6mm carbide mandrel. I have tried all turners from Pumpkin to K&M but this works best for me. Take a cut, then adjust the screw and the dial indicator indicates cutter movement. This is pretty much foolproof. These are no longer available as Fred Sinclair passed away.
$200

PMA neck turner with 22cal carbide mandrel.
$175

Or both for $350 inc postage.