There do seem to be the odd variation from country to country - probably down to different licensing and Hasbro offering up standard stock art which different countries could adapt as suited their preference. Hence why you can sometimes get frankenstein combinations of different licensees, different artwork and different finishes.
However, as Sebby says, a lot of them were either well used or of dubious quality as they dont tend to show up in perfect condition too often.
I think the shipping is what keeps their price low often on sales. They can be tough to price as often when for sale they are being sold along with ponies - I have seen them as low as a couple of $ and as high as $25 so its a pretty wide market largely influenced by condition and the price of end shipping.