I think I’ve maybe paid for 5 apps since I got my phone in 2011. Two were running apps, a period tracking app, Words with Friends Pro and probably a photo editing app. But most of those were paid for with iTunes gift cards, so I wasn’t actually spending my money on them.
An app would really have to prove itself to me before I’d spend money on it. I’m much more likely to buy the ad-free version after I’ve used the free version than just pony up the money up front.