Sony have announced the American prices on the PS Vita specific memory cards. They may look a lot like SD cards, but they're not.
The cards will be released as follows - 4 gigabyte ($30), 8 gigabyte ($45), 16 gigabyte ($70), and 32 gigabyte ($120). Pretty much double the price of corresponding SD cards.
There are currently no prices for the European market, but the typical conversion rate from dollar is 1 dollar = 1 euro, with prices in pounds a bit below that.