If you could find it at Harbor Freight, it would be $149. If you had someone with extensive cabinetry and sheet metal experience make it, probably $2000+. Since a SB computer can be had on eBay for $150, it seems a bit extreme.

I've had my SB since 2013 and use a computer that doesn't need a fan. As long as you use standard dust collection practices, such a cabinet would likely be overkill.