To open a sportsbook, one must have a detailed business plan and access to sufficient funds, which will be influenced by the target market, licensing costs, and monetary guarantees required by the government. The expected bet volume and marketing strategies will affect the needed funds.
The hangup is that in CA, all gambling outside a licensed gambling establishment is illegal, as is the facilitation of collection of those bet debts. You can be convicted of a felony for even setting up such a site and handling the first transaction or even offering your services to the public.