I do think prices will level out. Now where they level out I don't know, but they will calm. Things are still settling from the massive shift in the hobby.
I mean in the last 15 years we've seen the death of arcades, the death of Bally Williams, & now all the games are still settling into people's homes, which is a new thing that has never really happened in this hobby. At least not to this extent.

Also you got the huge role the internet plays. Thanks to the internet, I can now pinpoint exactly what games I think I would like out of many hundreds, & I can usually get whatever title that is. Go back to the 80's, I wouldn't even of had a clue what games existed other than a few. Let alone know how to get them.

So, thanks to word of mouth & games being hyped on the internet, for whatever reasons a game like MM appeals to just about everybody, & everybody wants one. Supply & demand at that point. For me, that is a rich mans game. Paying thousands more for a game that might be a little better than another.
I'm still jealous, but hey the great thing about todays market is that there is room for all sorts of budgets to get involved, whether you have $500 to spend or $15000.

As this trend continues, & things settle in a bit more to this new way of doing things, I fully expect some of the crazy price jumps we see to level out. More people will have a better idea of the actual value of things & all will be adjusted accordingly.
& until I hit a higher pinball tax bracket, I'll continue to be more than happy to swipe the great yet cheaper games that many others somehow overlook. Btw, I think if prices on games like MM do end up dropping a little, I do expect prices on solid B titles to go up as well. It makes no sense to me that some solid games can be had sometimes for the price of just a playfield on another game.
There are people out there who would pay $100 for a piece of bubble gum that somebody scraped off the bottom of their TZ, because it touched royalty.