If you're going to throw a great casino night event, it's going to cost some money. Hiring dealers, renting gaming equipment, buying food and beverages, decorating your space -- it all adds up. It's best to decide what your budget is early on and then back your way into what you can afford.
If you have a limited budget, you won't be able to have it all, so you'll need to prioritize what is most important. This is true for any party, but especially true for such a specifically themed event like a casino night. Food, drinks and décor are all important, but for a casino night, the top priority has to be the games. Put that at the top of your list, and then see what you can afford in the way of professional dealers, hors d'oeuvres and the bar. And remember, requiring your guests to "buy in" for the gaming can also help cover a lot of the costs.