My most memorable York purchases would have to be the prewar sets I've pieced together.
The first one was started at my first York Meet, in the Fall of 2010. On Thursday, I found a Lionel/Ives transition set of freight cars for $100 (the 1717, 1719, and I forget the caboose number right now). Well, the seller said that the 258 that came with it was shot, so I was on the hunt for an engine for this. I hunted the rest of the day, and didn't find one. The next day I had tests at college, but after they were over, I blew off the rest of my classes (very rare for me) and made the two hour trip to York. I searched for a 258 to be correct, but found a nice 262e for $160. I tested it and the e-unit stuck. The man talked me through the repair, gave me his card, and told me that if I couldn't fix hit, I could take it out and he would fix it at no cost. This engine was my first e-unit repair.
This left one car that I wanted to get; the Ives 1708 cattle car. I couldn't cheap out and get the Lionel version with this one, since Lionel didn't make it. I searched and searched for a decent one that I could afford, until I found it in an original Ives set at 2014 Saturday Spring York (who says you don't find good stuff Saturday). The set was in rough shape, the engine had mechanical issues, but the cattle car was fairly nice. I bought the set for a fair price, kept the cattle car for my set, and traded the rest of the set here. This set is one of my favorite ones to run, and a regular under the Christmas Tree or when we have guests.
As if fate, the other set is a passenger set. At Fall York 2013, I came across a Lionel 2640/2640/2641 set in C-7+ condition for $160. It was about 3:30 on Friday, and I needed an engine, since I had none with the box couplers. I am almost running up and down the rows looking for a nice engine for a decent price to pull these cars. I came across a 224E with 2224W that wasn't quite as nice (a few smudges and the letters are a bit faded on the tender), but was still in good shape. The guy said everything on his table was 50% off (it was about 5:30 at this point), so I got it for $75! It's another great set. Unfortunately, this is the best photo I have (it's the top set)