That price is very much justified in my opinion. First of all there is of course the issue with the economies of scale (the more your produce the cheaper it gets). Secondly, FP2’s design is simply genius!
Just today I helped someone troubleshoot their FP1 and we exchanged motherboards for a while, etc. If you have ever opened up a phone that is not designed to be repaired, you know how tedious that is. After unscrewing and rescrewing all the different parts several times, you lose your concentration, forget little parts (exterior power and volume buttons…) and wish that all phones were built in such an uncomplicated way like the FP2.
battery camera is the smallest issue here! Much more important is that FP2 can easily be troubleshooted and repaired. So it’s way easier to stick to it for a longer time.