I think you can start with a budget of about $1000 so have a full functioning website. If you are not a developer, then you will need to hire someone and so that budget could ballooned. But for the a grand scale project like gambling sites your budget could go as high as $50,000 or more to have a fully functioning site, bankroll not included. Then you have to pay for marketing and advertisement as well. So you see, having a plan is good, but executing it is very different as their are a lot of things that you need to factor in order to have a successful business online. Don't believed online marketers saying that it has only cost this much amount, it took them years to established themselves in the business.