Does it cost more to build an iOS app than a web app?

Yes:

1. web apps don't need an expensive development environment. So you don't need to buy or rent a mac just to submit the app to apple

2. Tools are free, no 99$ fee for ji'ust the right to submit apps.

3. No person can reject your app because you violated an vague rule or are thrown out because apple provides an very similar app.

We have a few web apps which are really PWAs. Due to Apple’s poor support for PWA discoverability, we also ship as an iOS “shell” app that loads the PWA. We haven’t had pushback from Apple on this. It has the advantage that we can still develop this is a web app while being able to publish in the store. We also have options if Apple were to change policy in the future since our apps are web first.

The primary cost differences I have experienced come with maintenance and fees, not the initial build.

Maintenance = iOS version updates, dependency upgrades, App Store requirement changes, etc. have been costlier and more out of your control than with web apps. Fees = the App Store's 15-30% fee is more expensive than using a web payment processor.

Shrug maybe. In general I think you can get a decent front end webdev cheaper than a comparable iOS dev. Even as an iOS dev, I think most iOS apps should be mobile web first or instead. I've seen a few that are nearly abandoned for webapps.

I've never developed for iOS, but I think building a web application is relatively simple.