Good thought out response, Piece Maker!
My only compaint related to cost of unis is the need to have at least several. A basic mtb can be great at off road, riding around town, some trials and tricks.
Still, all four of my unis together cost less than half my last new mtb.
Pricing Strategy
I am a business owner in HVAC. I can buy a 35/5 dual run capacitor for $5, and I sell it for $52, which is the lowest price among my peers in this area. I can buy a compressor for $600 and I sell it for $750. Why?
I have to make $X during any given billing cycle to keep my company afloat. I can replace two compressors in a day, so that’s about $300. I can probably replace 6 capacitors in a day. That also comes to around $300.
Very over-simplified, but the concept is there.
The dynamics are surely very different with UDC, but pricing strategies are often determined along similar lines. It takes just as much time to package and ship a bare frame as it does to ship a complete unicycle, and, at the end of the day, they have a budget to reach.
Of course, the other reasons listed make perfect sense. I just wanted to toss in a “he who sets the prices” perspective.
That’s true. It’s not really a NEED need, but you can’t get anywhere on a Trials, and you can’t jump around too much on a decent Road unicycle. If you like multiple disciplines it’s not like the old days, where a 24" would pretty much work for everything. 
Remind me not to buy your last new MTB!
That’s cool (no pun intended). One of my local riders out here is also an HVAC business owner. 
And you definitely have a point about balancing labor and necessary costs to keep the business running.
Having gotten back into bikes after moving to the Cascades, all I can say if that unicycles are dirt cheap compared to bikes.
I have two FS bikes, they are good bikes, but neither is the most expensive, but they were many times the cost of my most expensive uni; and I build some nice unis.
Yes, you do pay more for uni parts compared to similar bike parts because the cost of production is higher; fewer sold, so the cost has to be spread out over fewer pieces.
That said, all of my unis together are not as expensive as one of my bikes.
Uni resale is also better than mountain bike resale!