At one time Stanley offered a smaller pin for the #42X to use on finer teeth. Many people have a second set and file the pin down for use on finer teeth.
Prices can be crazy, just look at the difference between the two #42Xs listed here:
#42X Saw Sets.jpg
Even with the high shipping my first guess was it went fast. Looking into it the seller may have killed the deal and re-listed.
One of the tricks for getting a good deal on ebay is to keep looking and change up the search to look for listings where the person doesn't know what the tool might be.
Yard sales and junk shops can be your best place to find something like this.
jtk