This design will be pricey regardles of who makes it if you want to maintain the performance of your GPU. The PCIe riser card required is $80+/- a few bucks and the chasis itself is aluminum which adds to the price. Lastly he is in Germany and has to work with German electronics requirements which he needed to pay to get established. These are all costs associated with building this case. You can't blame the man for keeping a small % for coming up with the idea, implementing it, and spending thousands of dollars in prototypes and startup costs.
If a nuc is what you want then get the skulltrail nuc and get an external gpu - thunderbolt box and you will have a tiny computer but the external thunderbolt cases are $150+ so either way you are paying a premium on the product.
There are a few DAN A4 SFX look alikes in this forum but they only take mitx gpus.
You pay for what you get. You could probably have someone make an acrylic version of the case but the riser card will be expensive as Dan got them at $80 for an order over 1K so your order of 1 will be more expensive.