I've been working hard on the next version of Growth Gecko which will help you find emails for search results on LinkedIn. Doing this cost effectively is tricky because LinkedIn doesn't like you scraping them. Although there are services that offer this, they are pricey.
Anyway I've figured out a solution and found my first 18 emails!
I'm planning to offer a service to indie hackers (exclusively for indiehackers.com members initially!) to test their ideas using cold email outreach. This is one of the most cost-effective methods of validating an idea, but it's currently tricky to get right, and costly.
I'm planning to price it at $9.99 a month for 500 verified email addresses. At the moment, it's looking like I'll break even at this cost but I'm confident I can get this down with some optimisations.
If you're interested in being an early user for this service, let me know in the comments!