[petercooper]

No links as I'm not here to sell but I do seven figure revenues in the newsletter space from sponsorships by such companies looking to extend their audience (and most of them return so it must work most of the time!)

More broadly, I've seen a lot of people have good experiences with email newsletter advertising/sponsorship generally if they use the right publications and audiences (for instance I saw https://twitter.com/DenehyXXL/status/1326172165616570368 earlier today).

Podcast advertising is worth looking at too, but it mostly succeeds in a somewhat different way (podcasts seem to work better as a branding and door opening play than for trackable conversions despite what coupon codes imply). Reddit may also be worth investigating but you really need to play it right there, it's not a hugely forgiving place for sponsored items.