at first i change for single speed for the cost...
my first winter has a messenger, i had to change chain and cassette every month!
60$ cassette and 30$ chain, 90$ each month
now
i change my chain every 2 months and i flip my chainring and dx cog so i can use them with 2 chains.
so 25$ chain, half of 20$ chainring and half 6$ cog
so 38$ for 2 months