I have thought of this, the best party to be in any bet is the bookie
For a casino, you will also need to make certain you can afford to pay out a big winner early on. It may not happen, but if you got into trouble paying out, the business could be finished before it gets a chance.
Many of these risks can be insured, believe it or not!
There are a number of companies that will insure against certain big prizes being won. if you go to some local event, and see a new car being given away to anyone who rolls 6 sixes on 6 dice for 50p, you can bet they have insured against paying out. To make a profit, which is usually for charity, the stall only has to cover the cost of the insurance premium, not a new car, and the charity makes a profit even if the car is won.
It IS possible to get dirt cheap casino software, but it has a bad reputation, and only fools and newbies will play.
Startyourowncasino is offering its cheating casino software for a mere $10,000 for full ownership & source code. It can be rigged to prevent players from winning too much, so you don't need insurance
Hype would be a better choice, but again it has a troubled reputation. Microgaming would have very high start up costs, as well as the need to insure against wins of around 100,000 to 200,000 credits (pat royal flushes and non-progressive slot jackpots).
Despite all this, there is no guarantee of making money - quite a few online casinos end up in trouble, and a few go bust.