Yeah.. if it's empty.. then you've just taken most of the cost out of it

[for the controls/keyboard encoder/wiring/etc]
I built mine out of one sheet of wood.. it was about 22 bucks.. maybe less than 10-15 for everything else.. (wood glue, screws, had to buy new saw blade, couple of hinges)
I did purchase some crystallite (it's like lexan) for 28 also.. to overlay on top..
Guess to answer your question. is it a ripoff?? Yeah I think so. If you don't have any tools.. abyssmal woodworking skills.. no spare time.. then it might be worth looking at.. but if you want to go the pre-made route there are other alternatives also..