Going by the prices of the coaches already on sale, I would guess about £80, say $120 per coach. The Coronation Scot was a nine-car train so in the region of $1,100.
I should add that I have no connection withACE, axcepts as a satisfied customer.
If you Google acetrainslondon, then products and then coaches, you can see the sort of thing they do, very much in the tinplate tradition. Actually, I bought their Silver Jubilee streamliner car set to run with my Sunset LNER Class A4 "Silver Fox", since one gets the entire train for less than the price of one brass car and they look and run well enough for me.
