If an item wasn't a resource originally designated for the game then it'll be more expensive. Only the shop themselves knows the pricing scheme guidelines for sure, but I'd say since the development for past game assets was budgeted and pretty much paid for already there would be very little reason for them to charge a lot for them. It is conjecture of course but seeing as the mogstation exclusives have no guaranteed monies paying for them they'd want to bake more recovery into the price so that the cost of making them outside a constant income stream would be more likely to be recouped. It.. was not tied to a figure though? Perhaps I'm mistaken but it was theorized to be linked to a new possible limited statue but ended up coming out all by itself.
I wouldn't say "extremely" well. Though that's just being pedantic. What I mean is I've seen more than one or two people complaining on the forums about people spamming it enough to make an NM encounter rough. I've also personally seen more than 10 or 20 people on my server using the heck out of it. All super anecdotal truly, but enough for me to assume from my limited perception that if I personally have seen that many people using it and complaining about it that maybe one out of 100-200 people playing the game have probably bought it. That's not bad. To be absolutely clear the only thing I'm saying here is that the price isn't an arbitrary number set just to see if it works. I was willing to pay for it and I see value in it as have a few others and if you don't think it's worth it then by all means do not buy it and perhaps if the sales figures are low enough it'll go on sale soon. Saying things like "it should have... " and "SE is greedy" are childish though. Don't be surprised when a company tries to make money and don't expect them to give things away for free just because you don't want to pay for them.