300M is the entire US population of adults (and then some) numerically just so we’re clear. That’s too many emails to have been correctly opted in for anyone not on the fortune 500. Be really careful if any are in Europe, they have really strict standards now.
Offer to cold call for a company (Fiverr has a lack of native English which is essential for most B2B). Once you are good at appointment setting learn how to close. Commission only sales could blow your mind if you get good at it. Not entrepreneurship perse but 1099 at least 🤷