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
I would not recommend sending it to Blancpain. They have no original parts, no original shop drawings, and no special ability to take on a job like this other than perhaps the willingness to do so. The new Blancpain shares nothing with the old company, they just bought the name. What they will do is exactly what Jack has done for me, fabricate the parts. While the result will be similar, the cost will be staggering, far more than what Jack would charge (Probably less than $1,000).
Jim