Hello, Didace...
You're getting good advice, except for one bit I disagree with: Hemmings is NOT a good source for car prices.
Take it from a guy who's been searching for a car for well over two years. Allow me to explain: it's not that there haven't been great cars to be bought, it's just that for a while there my dream of ownership had to be put on hold while there was a downturn in my industry (cartoons), where such an indulgent purchase would not have been prudent.
That gave me p l e n t y of time to analyze the "for sale" market. One of my findings was that Hemmings is not a good source for gauging the market on classic cars. Two other bad sources: auctions and classic car dealerships.
As the "bible" of the classic car market, Hemmings is the most heavily-advertised and read publication of its type. As a result, it's ads are full of cars that are at consignment/classic car dearships and individuals who have unrealistic expectations of what their car is worth. When I read Hemmings nowadays, I laugh frequently at what people expect to get for their cars. What they ask for and the final price they accept for their cars must be quite different. In fact, I know it is: trust a guy who has called a variety of people about their cars, found that they had sold, and asked what they got for it. I also know a wide variety of individuals whose cars have been on the market for two or more years specifically because they are asking too much for them.
Consignment shops/classic car dealers typically list a car for 1-1/2 to 2 times what it is really worth. Some of these ads are in Hemmings. For example, there is a black/black coupe with a Webasto sunroof in Hemmings for sale at about $50,000. This car is in a consignment shop on the other side of town from me...it's in great shape, but other sources (listed below) claim that car is worth $30,000 or so MAX.
Auctions are not good for estimating prices, generally. Often they are quoted by sellers ("earlier this year, two mint '65 OTS went for $65K and $80K respectively at Christie's! I'm only asking $50K for mine! What a deal!") but such prices are due to very rich people buying the absolute finest specimens available in a highly-competitive bidding environment where money is a plaything...they don't reflect the purchases of you or I.
The suggestion to watch Ebay is excellent...THAT'S where Etypes of all conditions/styles are bought and sold on a fair, open market with the widest possible exposure. Look under "Completed Auctions" for cars that have sold already to find final prices. You'll find that what is paid for these cars on Ebay and what is asked by sellers in Hemmings is often RADICALLY different.
There are publications set aside specifically for the pricing of classic cars, and they're very detailed. I suggest the VMR guides...
www.vmrintl.com. Even better, there's the Standard Guide to Cars & Prices which exhaustively details the worth of a wide array of specific collector cars...my copy is edited by Ron Kowalke and Ken Buttolph. Maybe you can find it on amazon.com.
I think the Hemmings website (
www.hemmings.com) has a link to a pricing page too...I seem to recall it was not as detailed as the above guides.
Anyway, if you get two or three of these sources and show up at the seller's house with this documentation and average the cost out between the three and make an offer, I don't see how they could argue with you.
Make sure to entertain yourself by taking ads from Hemmings and Collector Car Trader and looking up the specific makes/models in one of the above guides to see what they're REALLY worth. Sometimes the price that is being asked is outrageously funny. (Example: a driver-condition Sunbeam Alpine that was worth about $3,500--the seller was asking $12,995.)