Drambuie is its own special sauce: there is nothing quite like it. It is based on blended scotch though.
I keep hearing people tell me that if you cut single barrel bourbon with 1/3 vodka it will taste a little like scotch at half the cost. Add just a little trace of vanilla and it is somewhere in the range but it isn't actual scotch.
Sorry to tell you, but you just have to shell out for Drambuie to get Drambuie.