Found some in McMaster Carr at under 30 bucks they aren't too bad, screwcutting them from where you're starting is going to eat that pretty quickly,.........unless of course it's for you.
The core on that size is .500" or .510" depending on clearance, either way there's not a lot of room to get a bar with 1/16" plus cutter protrusion in without losing stiffness.
When I make threading bars for that sort of job I use a bar say .025 smaller than the hole, then eccentricly turn it (it comes out sorta oval) for the cutter depth clearance, braze or clamp an inserted cutter in the end and use the parralell topslide method.
The bars seem that bit stiffer, needs better math than mine to yay or nay it though.
Take care. Sami.