I say it's just inflation because limited supply/high demand(but also limited wealth), prices on Ship 4 are just about the same and were also cheaper before myself and a few others begun to collect Mastery augments as future upgrades.
The Revival AC Scratches made the Mastery market take a backseat for a bit so it was lower earlier until we finished throwing Meseta at other players for fashion, now we're back at the mega slow Mastery grind...and even with 2 people it becomes a competitive market to acquire these sadly.
Not saying I'm right but this is my experience and what I think below :
I was originally paying 180-200k per Mastery II prior to the Revival Scratch, less people were going for them at that time too though because they were gearing Geant still and investing in a high Fixa Glissen(ongoing for some still) ...now that most of that dust has settled, some people are back at the Mastery market for future gains, but again, it's an extremely limited market so even 2 people can put a strain on the prices and cause you to pay a premium for it.
But uh...there is -still- always that one bum that is going to scalp it out though at the very bottom of the item search page.