It's strange that the Catapult is still expensive. One would guess that this one sellers want to get rid of.
One of the local stores just lowered the price for this expansion by half due to out of print, so I bought the only two left in stock. I was thinking of trying build up 6 copies of each non-rare expansion.
There's plenty of stores here that still sells it, albeit it's price is still higher than any other expansion (between 12-14 Euro). Compared to the expansions like Princess, Inns, and Abbey that sells for 11 Euro and the Tower at less than 9 Euro.