Hi dewi,
I am basing the cost on the lamp manufacturer's claim of 78 grams per hour, to run a mantle the gas will be run at a 'peep'.
For cooking you are going to use a lot more gas, I guess that you will have to measure your 'cooking' gas usage to come up with a reliable overall figure.
I use a lot of gas for cooking as I boil a lot of water for making numerous cups of tea, and the stove is pretty much at full lick for heating food.
For 2 days and 2 mornings (lots of tea\coffee in the mornings) I take three 220 gram canisters, I never get by on just two, but everyone will be different, I also use up gas for boiling water to clean pots and cups and personal hygiene etc., and have been known to fill a hot water bottle, I'm not exactly careful with gas consumption
.