The going rate for a working Berzerk of Frenzy boardset (same boards, only the roms differ), is $300+.
Berzerk/Frenzy had some major battery acid problems, thus spare working boards pretty much don't exist.
I suggest just trying to get a Frenzy marquee, and then using a computer instead of an original boardset. It is going to be cheaper that way, and it will also allow you to play at least 700 other games (while still using the original controls).