Here's a good one. Yesterday, there was a "50 Years of Amazin' Baseball" autograph event which took place inside the Ceasars Club at Citi Field. The Mets were selling some of their memorabilia at the event, and they had game-used baseballs for $20 apiece, or $25 if they were from Citi Field’s first season. I don't know what unattributed game-used baseballs are "worth" in the regular collectors' market, but during the season I've seen them for sale in the Mets' Amazin' Memorabilia stand for higher prices, and considering that the Mets ask $30 for brand new NON-used official MLB baseballs in their team stores (yes, I know you can get them elsewhere for much less), I decided this wasn't such a bad deal, and I went ahead and bought the two Citi Field Inaugural Season balls shown in the photo below.
(Yes, this is how they were presented. Loose in the basket, pick through 'em and take the one(s) you want. And yes, I did move the baseballs around so that the two Inaugural Season baseballs were prominent in the photo.)
When I got home, I looked up the provenance of the baseballs on the MLB Authentication website. According to MLB, the Citi Field logo ball in the middle of the tray, the right one of the pair, was used in the first “Subway Series” game played at Citi Field - June 26, 2009.
And the other ball, the one to its left, was used in an even more historic game. This ball, it turns out, was used in the August 23, 2009 game against the Phillies - the game that ended on an unassisted triple play, only the second time in the entire history of Major League Baseball that a game ended that way. This specific ball was not, of course, THE ball that was used in the play - in fact, it was used rather early in the game (“O. PEREZ THROWN TO S. VICTORINO, BALL IN DIRT,1ST INNING,” according to MLB) - but it was still used in that game.
Considering that the Mets have asked $500 for baseballs used in the final game at Shea Stadium, I’d say at $25 apiece, I got a pretty good deal.