buy home brewing kit to make kahlua
drink a gallon of apple cider so you have an empty jug
follow instructions in the kahlua kit
it's just like making beer or wine from a kit, just follow the directions. add this at this time, add that at that time, shake/mix, let it sit w/ an airlock on it, do this do that & voila - a month later you have about a gallon of kahlua for about $45. (well, plus the $15 apple juice lol)
the grand marnier, so long as it turns out well, is by far the best value... as to buy the real deal locally would cost $50/750ml bottle, so $250 for what you can make a copy of for $45.