a) They can click through to a Tinder site, where they subscribe directly.
b) They can click through to the App Store, where they end up subscribing via Apple's in-app purchases. Apple gets a 30% cut.
Assuming your $100 LTV from before, in (a) Tinder makes $97 and Apple makes $0 while in (b) Tinder makes $70 and Apple makes $27. Tinder clearly prefers (a) while Apple prefers (b), but by how much?
Tinder: they make $97 - $70 = $27 more in (a)
Apple: they make $27 - 0 = $27 more in (b)
This means both companies are willing to bid approximately the same amount, since their profit on winning, relative to what would've happened otherwise, is $27.