[cbr]

    less than Apple and Google charge

What your parent wants to do, "build an app to use on my own phone", is free on Android.

[Aaronontheweb]

It's free to build an app and deploy it on your own Windows Phone(s) too - you only have to pay if you want to distribute it through the Windows Store.

[yulaow]

It just changed some days ago

Since there, you CAN'T deploy a personal app in your wp8 because you need to unlock it first and to do that you need to have a developer account.