With most die-cast models, much of the value lies with the box. e.g. a model in the original box will often be worth two, three (or even more) times the same model, in the same condition, without the box.
Condition is also of extreme importance, a small scratch can halve the value of an otherwise 'mint' model. So it's hard to get an accurate valuation from any form of list (whether that be in a book or on the web).
The best way to get a free valuation for any form of collectable item is to take it to an auctioneer. Auctioneers are, of course, always hopeful that you'll sell the items through their company but they never impose any conditions when they give valuations. (I've walked into the London HQ of Bonham's, which is one of the top auctioneers companies in the world, and asked if someone could give me an opinion on the value of some maritime instruments. A couple of minutes later I got some detailed information, totally free of charge and without any obligation, from the same guy that people queue up for hours to see when the Antiques Roadshow visits their town. I've also had loads of other free valuations from local auctioneers here in East Anglia).
Most local auctioneers companies should be able to give you a rough idea of the value of your late father's models. However, this firm specialises in the field. They might be able to provide you with a valuation if you email them photographs of the models. (Obviously, you should hint at the possibility that you might consider selling them but, as I've stated, any valuation will be given without obligation):
http://data.bidmaster.co.uk/lsk/Model_dept.asp
Chris