Thought I'd share my positive experience achieving a very cost-effective
milled red-dot set-up
with co-witness BUIS; with shipping and extra insurance<$390.
There are a number of good sources for slide milling, but Primary Machine offers a 'package deal' 6moa Venom, Milling + slide Cerakote. They also offer packages with Viper but I discovered the Suppressor-Ready tall front Tritium Sight lines up very well with the sight markings on the Venom to provide co-witness BUIS. I liked this set-up on my P-07 so much, I decided to do a P-09 SR as well.
Here's the view from the 'driver's seat':