I once wanted to repair an older Ipad because the screen was cracked. The repair would have cost 600€ at an Apple reseller. A new Ipad would have been about 700€ at the time.
There is a reason why Apple is so against the right to repair.
Even their “self-repair” option nowadays is a load of bollocks. You have to rent the expensive machine, order a new part (which can only come from them of course), send out your part and wait before they will send the replacement part, then hope you don’t fuck up slightly, causing you to break the screen and you having to pay through your nose again to order a replacement.
So it only costs slightly less, but you will not have a phone for weeks.
There really is no reason third party hardware can’t be installed at the users own risk. But that would mean competition for Apple, and they don’t like that.