I do not think this will work as a strategy lol but if you want a rough guide, 0.4 mg nicotine ciggarettes would be marlboro lights, .6-.8 would be mayfair smooths, mayfairs, marlboro reds (might be 1mg in marly reds). 1mg is like horrible fags lol like palace I guess or some regals?
Use that info as you will but I dont think this strategy would really work. Could try I Guess. IF he wants to cut down and not quit (which is possible, I know lots of people, including me who have cut down and its lasted. Ive gone from 20 a day to 10 a day and its lasted for months), Id say just smoke less fags. He'll literally half his expenditure whereas if he moved to lights and smoked the same amount his spending would go up probably as marly lights are very expensive.
Fwiw, some smokers are not evilly trapped in a sickening and disgusting addiction to the perilous nicotine they cant get out of us. Some of us, god forbid, do not WANT to quit because we enjoy smoking