It is not cheap. It takes quite a long time. For your watch it is well worth it, now that these are all in the $3-$4K range in value. Basically, what it needed is a true watchmaker with the proper tools and the patience and willingness to take on a fussy job. It helps to have an original bezel to take the measurements from. The insert is possible to have recreated too. What is needed for that is a shop with a CNC machine and the willingness to do a "one off" job. Jack Alexyon of industrialwatchworks (dot) com has done a job very very similar to this one in the recent past. A friend needed to have copied a genuine bezel from my original for a very rare Bulova military dive watch (ours are the only two known examples, his was missing the entire bezel.) I also have had Jack make several Blancpain inserts for me. He is very familiar with the vintage Blancpains. His work is outstanding.
Jim