It seems weird to me that there would be Calvados in a Coq au Vin recipe, and the online version of the recipe says "Calvados or brandy" so I would definitely choose the brandy if I was doing it. It's definitely not worth $27, I don't think, unless you thought you would use the Calvados in other recipes, or, god forbid, drink it...LOL
From what I know about France, Calvados is from Normandy where they have a lot of apples and apple-flavored things. I know I've seen crepes flambéed with Calvados before, and it's used in other regional dishes too. Since Coq au Vin is a very traditional dish from Burgundy, though, I'd definitely use regular brandy, not "Calva" (they way locals refer to it, as I recall).
So, blah blah blah...what wallycat said!!
"In France, cooking is a serious art form and a national sport."