​What methods of finding cold email prospects worked for you?

So I’m looking into starting a cold email campaign, and I’ve decided on how I’ll handle most parts of it, but I don’t know where to find the 200-300 potential leads I’ll need. I’ve looked into services like ZoomInfo and CrunchBase, but they’re pretty pricey, and ideally I’d like to start with something much cheaper or free. Does anyone have advice to share?

If it matters, I have a specific niche (finance) and years of experience, but this is the first time I’m doing cold emailing.