| Platform | Retail | I paid | |
|---|---|---|---|
| Android | |||
| Play Store publishing fee | $25 | $25 | |
| Windows | |||
| Windows OS | $139+ | $0 | already have a Windows PC |
| Windows Store publishing fee | $19 | $19 | |
| Apple | |||
| MacOS device | $599+ | $450 | bought a used Mac |
| iOS device | $429+ | $0 | used my mom's iPhone |
| App Store publishing fee | $99 | $99 | annual subscription |
| This Website | |||
| Hosting (via GitHub pages) | $0 | $0 | thanks GitHub! |
| Registration (e.g. GoDaddy) | $0+ | $24 | annual subscription, varies based on domain name |
| Total | $1310 | $617 | |
Conclusion:
You can build an Android app on any type of computer, and it only costs $25 to start publishing to the Google Play Store.
In order to build an iOS app, you need Xcode, which is only available on Apple devices. And the publishing fee is $99 each year.
I bought a used Mac mini and built the iOS app. Xcode comes with an iPhone emulator, so I was able to double-check that everything looked good. But when I went to publish the app, there was an error:
"Your team has no devices from which to generate a provisioning profile."
You need an iMac AND an iPhone to put something on Apple's App Store. (Thankfully, my mom let me copy down her iPhone serial number for this.)
So, for anyone interested in cross-platform app development: be prepared to give Apple a bunch of money.