There were a total of 61,105 60s made. The only one lower than the high seat was a high-crop (212 of them).
I'm no expert on "rare". If I'm buying, it's always a "rare" item. If I'm selling, there are a million like it.
Just remember - If he's asking 10, he wants 8, he'll take 6, it's worth 4, so offer him 2.