From the groundup how to betting sites create a bankroll before the site opens?
Not as much as you think...
Domain $20
SSL $100
Dedicated Hosting $100 mo
DDOS/WAF $30 mo
Scripts/Coding (premade or custom) $3k-$5k
Bankroll $1000 (depends)
Total: ~$6200
You could cut a few corners, choose cheaper riskier hosting, buy a crappy pre-made script for cheap, less bankroll, no ssl... etc.
Crappy premade scripts usually come with an backdoor or it is unoriginal. Gamblers are more attracted to those sites who are custom made. The bankroll of $1000 is very low. You can try to find a few friends to be the investors. You would also need to pay a team of developers to help you with stuff of you don't have much coding and pentesting skills.