Those are expensive too.
I get why pinball mods are expensive. There is a tiny market out there, so returns have to be large to justify any sort of substantial investment of time or money. I just look at many of the mods and when many are 1/4 the cost of a machine I have to decide whether or not I want to put that money towards a new machine or a bit of bling to something I already have.
Right now I'm getting pretty full up in my gaming area though, so I'm starting to look at mods a bit more favorably. The biggest reason this one feels expensive is that we haven't seen the final product yet. If it comes out beautiful and proves to be a long-lasting product, I'm sure the price will be easier to justify.