Regarding the cost Asda are doing 10kg bags for ?17 and 20kg bags for ?30.
For the 10 kg bag that is 17 pence for 100 grams. I usually eat about 70 grams which would work out at about 12 pence. That's quite cheap in the grand scheme of things and a similar amout of pasta or even spuds or chips would probably cost more.
Cheers,
Paul