Even when gas checks were $10/k, I found it amazing that they cost what they did, meaning THAT much. Primers, which ere much more complicated ran about the same price as gas checks for a long time. Percussion caps are way simpler than boxer primers, yet they have trended above primers for a long time too.
Economies of scale would explain some of that, I think, but geez, man, not all of it.
Right now, I think everyone is asking more just because people are used to it and will grumble, but pay. I don't personally believe there is as much REAL cost difference as what we are seeing at the retail level. THAT part of the increases we've seen is artificial and the part we should be able to HOPE to see eventually dissipate.
There are a couple "new guys" making gas check makers now and the competition with the established few has prices which are getting closer to a thousand commercially-made gas checks. I know - more time with a tedious task, but it frees you from a merciless supply line, reduces dependence and adds yet another element to trying, testing, experimenting and perfecting (never mind the impossibility, the fun is in the trying) factor in shooting cast bullets. It's also rewarding to chunk out a hundred 'checks while between other tasks or ruminating on the next move on some task, because you start to accumulate something valuable as you go - like money in the bank or neatly stacked firewood.