@Raycuda brings up one of the most important points. It is very valuable to have the shop close by so you can make frequent in person visits (some unannounced!). You want to make sure you can see what is getting done and how they are going about it.
IMO all of the value is in that front cover. If it's broken, $100. If it's not broken, $1,000. That's just because I've never seen one that wasn't broken in person. Pretty sure the first person to sit in the passenger seat in 1970 broke most of them.
One thing I have found about NOS parts is that they are sometimes still around for good reason. For example, I used an NOS fender for my 70 cuda and the headlight bucket area needed to be reworked because it wasn't spot welded in the correct orientation. It probably sat on a shelf after they...
Do you know who manufactured these? I didn't know they made reproductions grilles with the part numbers. Of course, I am definitely not an expert in this area.