Unless the price of blu ray items has shot up for some reason it's possible that pricing it at £5.99 was a typo, which the seller corrected when they realised their mistake. It's a pity you didn't buy it as soon as you saw it!

If some sort of supply restriction is being exploited by sellers to charge artificially high prices this might be covered by eBay's policy on price gouging, but this seems unlikely. Price gouging doesn't apply where worldwide demand has raised prices univrsally - as in the memory upgrade I bookmarked for my PC a few months ago, but quadrupled in price withn weeks.