Quoted from rancegt:

I'm not sure when prices will stop going up, but it doesn't seem like they're going down very soon.
I bought my first machine in January, and I've been adding games as I find good deals. I just bought a Fish Tales last week. I'd never even played it and I wasn't sure I wanted to keep it, but it was a good deal and I know I can always trade into something I like better later. It turns out that I like it so it will stay for a while. My other games have pretty much the same story.
I also don't have any games with collector quality playfields. If you're trying to get in cheap, you might have to put up with some bumps and bruises. For the most part they play the same so what do you really miss? Having to nudge the ball over the mylar bump on Stargate's inlanes every now and then is worth saving $600 to me. After I build a reasonable collection, maybe I'll spend that $600 and have the playfield restored but I'll have fun playing until then.
This chart from Boston Pinball shows that the supply is decreasing while the demand is either increasing, or constant. If the yellow line starts to trend back up, prices will start to level off or go down. For that to happen, people would have to start dumping their collections. Can anyone think of a reason large numbers of people would do that?