Appraisal of unopened models

How about I just come and get them, problem solved? 

You might also try 3GUYZ hobbies......cjltd@adelphia.net.....out of Buffalo NY. Write to BobC

They buy large estate collections such as yours, and I trust them very very much! 

This site has the biggest assortment of old plastic kits I've found on the web:  http://www.oldmodelkits.com/ .  I don't know how much practical value it will be for this particular purpose, but it will at least give some idea of the prices such things can command.  This guy's prices seem on the high side to me, but the fact that he stays in business suggests that significant numbers of people are willing to pay them.  And I gather he'd be willing to consider buying the collection.

The prices of old plastic kits seem to range all over the map - sometimes for sensible reasons, sometimes seemingly irrationally. 

If any of the kits are Revell ones (as I imagine they are), an excellent source would be the book Remembering Revell Model Kits, by Dr. Thomas Graham.  The appendix contains a list of "collector's market prices" for all Revell kit produced before 1980.  A new edition of the book has just been published:  http://www.squadron.com/ItemDetails.asp?item=SH2992 .  Dr. Graham knows what he's talking about; I suspect those prices are as reliable and up-to-date as can be found anywhere.  He's published similar books about Aurora ( http://search.barnesandnoble.com/Aurora-Model-Kits/Thomas-Graham/e/9780764325182/?itm=3) and Monogram ( http://search.barnesandnoble.com/Monogram-Models/Thomas-Graham/e/9780764324819/?itm=1 ) kits.  The latter two are a couple of years old now, but surely the values of the things can't have changed much in that amount of time.  Those three books should be of considerable help.

I would suggest that you contact a local IPMS Chapter to see if there is anyone willing to help you appraise the value of the kits. There is a book (value guide), but given the ups and downs of the market it is not necessarily accurate. One of the best methods is to search eBay to see what each kit is averaging in price.

Recently there have been kit auctions from individual estates, some were conventional on site auctions, others were done as a store close out sale and others were handled by family and friends as eBay auctions.

There are also many individuals who purchase large collections. They post advertisments in FineScale Magazine as well as the IPMS Journal. 

Someone will chime in with other recommendations, that's one thing about this forum, the positive support!