$2500 would be fair. $1500 would be fairer to the buyer. $3500 would be fairer to the seller. And that is just my opinion. Ask 25 folks and you'll get 25 or so different opinions.
What you are asking is rather hard to nail down. Condition, location, rarity, keeping it in the family all play a part in determining values.
A buyer should NOT have to both buy AND sell an item.
Sellers often hold out for an "offer" which exceeds their real expectations which they quickly agree to and in a sense "out wit" the buyer.
If someone has something for sale and will not put a fair value on it, as a buyer, I point out all the bad points and costs of having the work done and use the "sellers technique" in reverse, offering a ridiculously low price in hopes of "out witting" the seller.
Another more tactful approach is, "it may be worth $200 or it may be worth $20,000. Where in that range are you willing to sell."
Ebay and price guides are only tools not answers to your question. The inability to see, examine, and possibly test the item can never be factored into a price guide or most ebay "used" sales.
Ultimately it comes down to this:
What is the least amount he is willing to accept?
What is the most you are willing to pay?
Once you and he work out those issues a sale or no sale will occur.
While recent sales of VERY good restored cars have taken place for $10-20K the trend has been they sell cheap and its easy to put more into a restoration then the value of the final product. Wagons are not at all scarce.
Your question is not an easy one for anyone but yourself.