Those cabinets would be considered custom by any shop. The equation always is:
Custom = $$$$$$$$$$
Material is not the only part of the equation. There is learning and set up time, possibly the construction of special fixtures requiring time and material that will never get used again, the chance for expensive errors because of unfamiliarity, and lost opportunities due to the extensive time to learn about a custom job.
There are lots of speaker cabinets out there, both assembled and in kit form. Will they work for that particular speaker? Probably not. Check ebay, Parts Express and Iwistao.
https://www.iwistao.com/collections/emp ... m-cabinets