This Fermo SAS 1/100 metal 747 model was missing an engine and sold yesterday on ebay for $315:
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=290565320186&ssPageName=ADME:B:WNA:CA:1123
The cost of having a model recast, plus shipping model to and from a foundry will add another $200 - $300 to the cost of this model, which puts the total outlay to the owner in the $500-$600 range. Which I guess would be the somewhat fair current value of such a model.