Here's the thing. While "most" of the tanks are rare, and thus expensive, there were a few that were uncommon, and (IIRC) even a few that were common.
So no, you are not going to find a German Tiger for $1. USD But you might find that Pz IV that came in one of the starter sets for cheap. You might find that US Sherman that came in one of the starter sets for cheap.
And a few of the light tanks (like the Stuart) go for a couple of bucks sometimes.
Japanese and Italian tanks don't go for the big bucks, regardless of their rarity.
But mostly, no, they are not all that cheap. And if you compare the price to get, say, three of something useful from ebay, to the cost of getting three of them from Old Glory (Command Decision line is always 40% off unless that has changed recently), and you save more buying the metal tanks. Of course, you have to assemble and paint 'em.
