reply.io (cheap) and outreach.io (better but more expensive)
Amazon SES + Sendy is cheap and effective but you have to make sure it’s properly configured.
However, be careful. The CAN-SPAM Act doesn’t apply just to bulk email. It covers all commercial messages, which the law defines as “any electronic mail message the primary purpose of which is the commercial advertisement or promotion of a commercial product or service,”
If you're planning on using email marketing I'd give this page a quick review and make sure you're on the right side of it: https://www.ftc.gov/tips-advice/business-center/guidance/can-spam-act-compliance-guide-business
CAN-SPAM enforcement has been 100% focused on the very large-scale spammers that are clearly fraudulent. First, a tiny percentage of emails are not commercial in some way. Second, most email providers have implemented protections from the type of activity that would raise regulatory red flags. So, if the number is in the 4 digits, and you're sending them with a reasonable amount of diligence that your content isn't fraudulent, you shouldn't have a problem.
We send a few hundred cold emails a day to potential customers whose social profiles have indicated their qualification, and have not had problems. One thing you should be _very_ wary of - if someone responds to your email asking to be removed from your list, you *must* remove them. Otherwise they can report you themselves and that _is_ taken seriously.
One more note: if the cold email campaign is aimed at investors, trust me, they do not work, unless you're trying to raise money from Nigerian Princes. You are much better served by focusing on getting a small number of high quality referrals to a targeted group of investors.