Thats basically the Unika 4U UK-4129 which can be had for ~70€
You do need to do some mods inside. Remove all the HDD trays, and make a new internal support for the cards (the default support you see in the pictures wont do).
Also, by removing the HDD trays, you lose support to screw the Frontal fans and you also lose support for the front I/O panel (usb, power and reset) so you need to put it somewhere else.
Well yes, there are plenty of "similar" cases on the market, but the magic of the RSV-L4000(4500) is that it seems to work without any major modifications.
Did you try modding the Unika case?
I've did one frankenmod of a CHIEFTEC UNC - 410F B-OP, but it took too much time and is not something you would do on a larger deployment.