Usually you need a table for every 20-25 quests. The main tables are blackjack and roulette. Craps and poker make good additions if necessary. The entry fee entitles a person to a set amount of chips and the aim is to end the night with the more chips than anyone else.
My organization usually gives prizes to the top three. We charge an entry fee of $20 and that entitles the person to 40 chips. For some people the 40 chips will last the entire evening but many others will go bust before the end. Their evening doesnt have to be over at that stage because they can buy back in for another $10, which gets them 20 additional chips.
I would recommend that you to limit the number of times a person can buy back in to two. This ensures that no-one gets carried away! The maximum they will spend is $40 (unless of course you have a bar!).
How much do you pay out? Well, thats really up to you but you should have a least one prize of $200. If you have 100 people paying in that nets you $2000 to start with, but it will more likely end up closer to $3000 with people buying back in. You will probably pay $300-$500 for the table rental for the night.
You stand to make between $2000 and $2500 if you have 100 people there. Thats pretty good for a single night and if youre a decent sized community organization you should be able to get closer to 200 people. If you're not adverse to the gambling aspect of a casino night then go ahead and add it to your list of nonprofit fundraising events.