AWS can set their own price (or subsidize it to keep people on their cloud), more efficient per $ is not really a good way to judge how good is the chip, though it is a good measure for how much money will stay in your pocket.

Sorta - There is translation layer in software but the reason the M1 is so fast at executing x86 code is that it has hardware support for switching to the x86 memory model. This is something no other ARM processor I'm aware of has.