Ever see what a shop charges for a custom fiberglass enclosure? My last quote in 2008 was $1,000 just for the custom fiberglass enclosure, and that price was based on me purchasing the sub from the same shop.
To the OP, another thing to keep in mind is that the Stealthboxes are generally oriented towards SQ over SPL. In other words, if you want something loud, the Stealthbox isn't the right tool for the job.