woofgang, I can tell you the cost of block salt per 100 gram would be even cheaper having extrapolated the wholesale cost of vacuum packed salt manufactured by British Salt. It works out at around a quarter of the cost of the same weight of salt out of a typical supermarket own-brand salt drum even after factoring in a profit for the retailer.
It would be wrong to say that we are using less salt. You may well be sprinkling less on your chips, but the reality is that we are eating more and more processed food in the UK each day, virtually all of which requires a year on year increase in salt production. British Salt don't package the stuff in 25Kg and 100Kg bags and then onto pallets for nothing - it doesn't go to be packaged for supermarkets in 500g/750g drums, it goes to processed food manufacturers.
I'd suggest you to take a look at the annual production figures from members of The Salt Association for different viewpoint on the amount of salt produced annualy. Incidentally, you can dismiss any idea that the increase is due to use as water softening agents,road salt and export. France produces far more and far cheaper salt than the UK and France is not alone.
There are in the UK a number of organisations with influential academics, physiologists, nutritionists, food scientists etc that would have you believe that we are consuming less salt. These include CASH and WASH amongst others. Historic data will show that whilst the work of these organisations is admirable, they have had little influence on overall salt consumption. This is in part due to their inability to explain in simple terms to the public the difference between "Sodium" and "Sodium Chloride" in food - the maximum recommended intake of these differs and seems to continue to be a major hurdle that cannot be simply explained to the public. Food manufacturers take advantage of this confusion when declaring Nutrition Information. EU and FSA labelling regulations on these declarations has also not helped.