OK maybe not the cheapest out there, but the cheapest I have come accross a full retail packaged Sandisk microSDHC on the high street.
Reduced from £14.99 to £8.97 & now £7.48 (plus 14p in clubcard points so £7.34)
Plenty of stock at Goole Tesco
Also have the 2GB cards on sale for £4.00 each
Also available at Tesco.com I believe