I don't get it either, Roger, but in the used book trade, it isn't at all unusual to see such enormous price ranges, in my experience. It's an uncontrolled, international business and sellers are free to charge whatever they think the market can bear, but in the internet age, it's so incredibly easy to price shop worldwide that logically you'd expect much less disparity between high and low for a given title. (Excepting items that have collectible value of course, such as some first editions, author-signed copies and the like).
Personally, I highly recommend
Abe Books as a place to start your international used/out of print book search. Ironically, I've found that out of print Aussie books are usually cheaper from overseas dealers than local ones!
I would buy locally but......
