This forum has great potential for linking arboreal practitioners together. One service would be to post the regional value variables for tree appraisal. Consultants are good about sharing this information, but those of us in the sticks don't rub elbows much.
I am working on a case of several lost 20' tall Douglas firs that are between 4" and 5" in diameter, measured at 12" above grade.
The nurseries in this remote location are the source of 3" potted trees 8' in height at $74. These are the largest "commonly" available replacement stock. The difference would be the increased caliper, plus a consideration for the height differential. This would be installed cost plus one or two inches of increased diameter.
How far is 'nurseryland' from your area? What kind of delivery charge gradient affects availability and feasibility of obtaining replacement stock in your service areas?