Normally £10.99 each.
Same as the promotion on Xbox Live that has been running since Monday:http://www.hotukdeals.com/deals/call-of-duty-mw2-stimulus-package-a/770754
The promotion will be running on the Playstation Network (PSN) from the next store update (which usually is applied... today?) for one week.
This information is based on a recent twitter update from Playstation Europe (PlaystationEU).https://twitter.com/PlayStationEU/status/26453570515
For one week only from now, the Resurgence and Stimulus map packs for Modern Warfare 2 are half price in PlayStation Store."
The deal link goes to the Playstation Store page and does not have any additional information about the promotion.