Depends. You need a lot to start a licensed sportsbook or casino.
The software for the website, the Anjou license (cheapest) seems better than Caracoa for cost now and the ongoing maintenance. Coupons, payouts, marketing and other fees. You are looking at 100K regularly to get this type of thing up. I have looked into software providers. You could start Belize IBC/Costa Rica Co and hold the license, even the cheapest is 17K a year or so.
Software provider like Betconstruct take a rake of profits too. There is one lifetime software for casino games package, costs a lot 40K for the package and you host on VPS and setup the rest.
I could start a unlicensed book probably for 2K and run it with big profits quick, though that is not in the law, so I do not try it. The states are slowly opening up to gambling because they spent all of our money on waste. Still its not a pretty picture. Now some the software providers have license and you would get sub license included I hear, this sounds good though though outfits want a cut aka rake of 10% of profits or so.
The sportsbook and casino software are quite automated for taking bets, compared to manual methods of the past.
I have my own custom card game I am trying to patent with a utility patent, hopefully it gets put on tables/VP machines and more of a product line after.
Custom casino game quote I got for development is 25K, then its a VP game or some such
From a player standpoint I know most the games inside and out, you could even say Im on the level of an advantaged player. Ive been playing since 8 rummy, poker, blackjack and more (war/bunko). When you get so good at dealing, shuffling such you almost become a natural card mechanic, especially with some counting techniques.
Cheapest you could maybe do it 25K on a sub license with a split, that estimate may be low though so check providers. Good luck.
I ran the numbers a couple times. I can create custom Sports App, though to run it legit I would need to get the license and have the application certified.
Advantaged Play methods:
-Coupons/Match | Free Pools / Giveaways
-BJ Counting/Baccarrat Counting
-100% VP Machines - Comps
-Arbitrage | Picks * / Misc Adv. Methods for Sports (+Picks resell)
-Skill Games (Rummy/Poker/Custom)(Backgammon)
-****Dice Setting (Not fully proven, am testing)