The flange I had waterjet cut cost me $70 AUD (ie $50 USD) to get made out of 12mm Ally. Mine is for a BP05 head and has larger port holes for the Honda manifolds. Files are here: https://lastpixel.box.com/s/vwdgkpy65ok26o0gykhd984iew4my92a
Given the welding, grinding and then surfacing of the flange after it's attached to the intake, I don't think there is much need for a pretty CNC one. You only really need that if you are making a manifold from scratch and the runners can slot into the recess.
Just a couple of notes from when I did my intake. The flange shrunk approx 1.5mm when it was welded to the runners. This meant the end holes didn't quite align and needed some filing. I would move them out or oversize them slightly next time. This may be different per manifold and welder.
All port sizes need to be undersized vertically a little due to the angle of the runners and the head. Once welded these angles need to be ground into the flange. Also, the end two ports need to be undersized horizontally to allow for the angle of these two runners. (NA8_Inlet_Flange_for_Honda.dwg has the end ports reduced by a few mm)
I made my flange out of 12mm so it could be surfaced flat to approx 10mm. You do get some bend in the flange when welding.
If anyone wants them, I can make a CAD profile to suit your application. Just need to know what head and what intake you're going to attach.
edit: The CAD linked above has room for triangular bracing to be attached at the base of the manifold which is why it has the larger flats on the bottom of the flange.