What's a good CPL for paid ads to newsletter?

Title pretty much says it all lol. I’m running Meta ads, one campaign promoting a short story lead magnet and one promoting my Kickstarter (sign up for my newsletter to be notified when I launch). Reader magnet is currently around $7 CPL and Kickstarter is about $2.50, which I’m pretty sure is great. I’m wondering if I should turn off the reader magnet one and increase the budget on the Kickstarter campaign. But if $7 is a reasonable CPL I might keep it on since those readers could go and get my currently available books. Thoughts?