He shouldn’t go to a gambling den at all, its full of pritzus and other bad influences, he should gamble online from home. Then you can serve him his drinks at the cheaper price.
Tell him that if he agrees to only gamble online you will double his monthly budget to $1200. I know you cant afford it but arent you willing to give up $600 for his yiddishkeit? How can you put a price tag on the zechus of sparing him all the nivul peh that he may hear in a casino?