It will probably be much harder to find a supermarket which doesn't sell calvados than to find one which does!
I've seem it in fairly cheaply in Lidl (but their product ranges change so often that I couldn't guarantee that they'll still stock it). Tesco will sell you a 50cl bottle of their own brand calvados (VSOP quality) for £11.61.
Sainsbury's are only slightly dearer:
http://wine.mysuperma...Dauge_VSOP_500ml.html
But for a taste of luxury, buy this one (which is on special offer:
http://wine.mysuperma...e_XO_12yrs_500ml.html
Chris