Quoted from Whysnow:A game with around 500 made is about the highest that will ever be considered rare, but based on time and life factors it needs to be around 100 or less still in existence to really be 'rare'.
I've been in the hobby about 7 years, and I think it really depends on the title as well. As Whysnow said, truly rare is probably 100 or less, or maybe even 200. But as a person who loves horror things, especially anything vampire, I wanted a Bally Vampire badly when I realized they were out in the world. One of only 3 true U.S. produced vampire pins (BSD, Stern Dracula and Vampire), I thought it wouldn't be that hard to find with a production number of 799 units. 6 or so years into the hobby, I had only come across 3 or 4 of them, including the one I finally bought from out in Louisville last September.
Although a production number of 799 is higher than most on here are considering as "rare", here's what I also consider:
250 or more of them probably found their way into landfills....destroyed, discarded, long forgotten.
100 or more of them were probably parted out or combined with non-working examples so someone had a flippable game.
50 or more of them are probably sitting in a barn, operator's warehouse, shed, garage or basement rotting away.
So that leaves around 399 games (conservatively) in "circulation". However, only 18 Pinsiders have the game in their collection, and 24 have it on their wishlist. On Pinball Owners, only 16 games found. Where the hell are the rest of them? Given the frequency they come up (never), how many people that have them and are willing to sell them (none), I think even with production at 799 it's a pretty rare game, and I would estimate that there is actually less than 100 left in the world.
I think this would hold true for a lot of games with production less than 1,000 or even 1,500 games...so the production numbers themselves cannot be relied upon as showing a game's true rarity. Just my two cents.