Setup is built around a 8 GPUs per daughterboard(the actual board I'm building). Two of my boards are connected to the mainboard (~$150). My current estimates are around 150 per board..so 300+100 = $450...I guess my estimate price is a bit too low for you then  huh The current board I'm testing can physically connect a total of 18 GPUs since it has two extra PCIE slots...youll will just need risers for that last two (there is a possibility a future BIOS update I could make it to post with 3 or even 4 of my boards for a total of 32 GPUs, but I'm just working on 16 for now...plus I would need to work closely with miner devs for anything more than 16...I have slowly hinted them improvements which they have already implemented for multi GPU setups in the past year).
Also the board has status LEDs per GPU lane...if a GPU goes down you'll know right away which one it is, and yes if one GPU crashes the board will still work. This is no different than any other mutigpu setup, other than it having just more GPU lanes. Your doing something wrong if one GPU crash brings down your whole system.
Keep in mind that this price is mostly dependent on the quantities I can order for parts on the first batch. Obviously more boards = less price per board. I am also pretty much charging the cost of components + a small profit margin for me. The design + dev + testing + prototyping etc is all done by me so thats why I can price it so low.