Indeed not the original board and as pinballer1 noted the boards you need have is for the early system 6 games. The later double boards (sound and speech) you'll find in Black Out, Gor Gar, etc.

One additional remark: sound roms are easy to find and can be purchased at different stores

They shouldn't be that difficult to find as there were so many produced in the early eighties!
$50 seems reasonable to me, but both boards should be at least working!

Good luck, Fire Power is very nice pin to own! I had two in the past, one with drop targets and 7 digit display installed.