Interesting idea, but I think you’re facing some tough competition.
For example,
MailChimp offers this for Free
Up to 2,000 subscribers and 12,000 emails per month
SendGrid
EMAILS PER MONTH
40,000
$9.95/mo
EMAILS PER MONTH
100,000
$19.95/mo
About the only real positive of your idea that I can see is that the recipients will be a targeted audience.
I think demonstrating that the cost for your “improved chances of conversion” is worth it compared to the no-low cost of bulk emails with a higher fail rate will be what you will need to sell for the idea to work.