At a supermarket you can pick up a new release CD for under £10.00. A high street retailer may be a pound or so more expensive.
Back catalogue CDs retail at anything up to £14.99 (I've been wanting to buy the Wolfmother CD since before Xmas but won't pay that much for it!) but ex-chart CDs can usually be found for much less. Beatles CDs are usually over the £10.00 price mark whereas you could treat yourself to the entire Radiohead back catalogue for less than £30.00!