Labor on a WPC driver board would have been the biggest cost factor, there's just a huge amount of parts to hand-stuff. The ironic part is that manufacturing that board today, to the same design and layout, would probably be much more expensive. There's very little automated thru-hole equipment out there anymore in the field, so there would be a lot more hand labor, and lower volume production would mean per-unit component cost would be much higher.
As to the sound boards..... the board itself is easy. Rick has told me in the past that ALL the board data is available, and bare boards can be made without any issue. It's the impossible to source components that are really holding things up, and as time goes on that's only going to become more pronounced as more thru-hole parts go obsolete.
I know there is a strong preference toward making functionally identical to the originals but an increasing number of designs can only be reproduced via redesign and modernization.