regarding board-swap FSD upgrade costs to Tesla...
I imagine these can vary massively depending how skilled they get/how easy they make it.
Years ago I was a PC/Apple Mac hardware engineer. Back then, changing a typical PC motherboard would takes hours. literally hours of unplugging connectors, undoing screws, labeling stuff, disassembling bits, and then reversing it all.
At the same time SOME (by no means all) apple computers (the ones we called pizza-box-style, cant remember the model), could get a motherboard update in about 20-30 seconds top. You could train a small child to do it.
Hopefully Tesla were sensible when designing the hardware, and its an easy swap. The costs of this sort of thing really can have an order-of-magnitude variance.