Ahem! Stand aside neophytes, a Kentuckian has just entered the room.
Nearly all bourbon is made in Kentucky, so bourbon is something we know a little bit about.

Who, while bourbon is in fact whiskey it has a distinctly different taste unless you're like these guys, who apparently buy their whiskey from the Bargain Liquor Barn in plastic bottles. Here's everything you could possibly want to know about bourbon: Not all whiskies are bourbon
Another thing to consider is that the recipe was crafted using actual bourbon, not rotgut or blended whiskey, so substituting an inferior whiskey could compromise the taste of the final product. Unless the recipe calls for a cup or more see if the liquor store has some of those little one jigger bottles of it and buy just the amount you need, they hold about 1-2 ounces each and generally cost about $1.50 apiece.