Used to be, say 25+ years ago, a simple starting point was a base price of $50 for almost any aircraft ID in 1/72 celluloid acetate like Cruver Design Center, etc...., and then add on $25 for each pair of engines, and another $25 for a special feature like intact landing gear, or floats- so a Cruver B-17 would start at roughly $100 {actually this is a bad example as the B-17 is very much sought after and the prices were over $200 The C-47/DC-3 also gets premiums}. Add a $50 premium for any flying boat.
Over the years this simple starting index went up to over $50 but recently had lowered. Still it could give you an idea.
There really are not many, if any, 1/144 wartime ids around made by American firms or others for that matter. 1/200 was a scale favored by the Luftwaffe {made by Wiking in plastic}, and there are two sets of 1/432 wartime ids, one by Cruver in plastic, and another by Comet in white metal. Both of these sets had holes in the fuselage for hanging or mounting. Postwar examples generally did not have this feature.
You can also find IDs at militaria auctions.
My collection is being sold by Affiliated and for the next year there will be examples for sale
here is one going this weekend
http://www.liveauctioneers.com/item/155 ... tion-model{do not pay attention to the estimates, they are way too high, but I expect this model to sell for $135 or so. it is rather hard to find intact, and no repairs.
BTW, bid on the net in advance, and you will need to register first.
Also 13 NOS boxed mainly postwar IDs {some rare Setco etc} will be auctioned of soon at
http://www.stephensonsauction.comCall them to find out when.
In general, you will find here on this forum the most knowledgeable ID collectors around, and it is much better to deal with them than some unknown on eBay. People like Dennis Ramsey and Bryan Brown frequently have duplicates available. I have bought many from Bryan Brown, for example and have been very happy. He will guide you well.