Agree on this one, and for other items of interest, say refrigerators and coolers. Large Dometic electrical coolers cost about the same as a higher quality full-size refrigerator. Small 12/24/110v refrigerators are over-priced in my mind too. RTT's are way over-priced. The list goes on.....Comparing a DIY camper "expedition" or not, (with free labor and different build standards), to a low volume, professionally made (and supported) rig is somewhat ridiculous. Companies like Earth Roamer have to deal with warranty support, liability costs, and the overhead that comes with a shop, business, and full time staff. I know this site tends to skew towards DIY (as do I) but don't fall into the elitist thinking that everyone must have a DIY rig to get a good value, or to actually enjoy using it.
Some of these rigs are overpriced based on raw materials costs and features. However finishing work (to make it pretty) is time intensive, taking many hundreds of hours. All of which have a labor cost, and overhead as they take up shop space. This is part of the reason that these live-aboard rigs with lots of attention to detail and appearance are so much more expensive than utilitarian type support vehicles. Finishing work accounts for some 25-45% of man-hours on these type of builds.
Of course there is significant profit margin. To operate a successful business with such low sales volume, you need big margins. (Similar to performance/luxury cars). In order to get that margin it is often necessary to target specific market segments.