If we sold CDs for £5 we'd make a dead loss against what we paid for them, never mind all the other overheads etc.

We do sell for less than the Wild Goose RRP (£12 vs. £13)
We offer a discount if you buy more than one (£10 each)
We charge purchasers exactly the same price (including quantity discount) via the web site, absorbing transaction and postage costs, which is really quite generous.

And to add to Tom's answer, look at it this way: the ability to make some profit from CD sales (and it's always a gamble - you never know how many or few will sell at a gig) means performers can charge a lower fee that they would otherwise have to, and there's already pressure, from club organisers to keep fees (often unrealistically) low.

Anahata