Cheapest case in England (or the UK) would probably be the Yoctopuse design
if you buy it off eBay (see elsewhere).
Postage and packaging: £1.00
Once you have it bolted together it is very solid.
I throw mine in my bag every day to go to work without anything else around it
and it's not even marked.
They have sold over 1000 of these and it's easy to see why.