The "economy" is D&D is a game balance tool; allowing the players to pick and choose magic items without them overpowering the monsters. It has nothing to do with daily living expenses.
For all the non-adventurers, the Economy is a case of trying to stay ahead of starvation. For anyone to survive, their income must at least equal their outgoings.
I think that a nice system is as follows:
a labourer's household needs 1cp per day
an artisan's household needs 1sp per day; it consumes twice as much as a labourer's household, and supposts 8 labourers' households
a merchant's household needs 1gp per day; it consumes twice as much as an artisan's household, and supposts 8 artisans' households
a noble's household needs 1pp per day; it consumes twice as much as a merchant's household, and supposts 8 merchants' households
a prince's household needs 10pp per day; it consumes twice as much as a noble's household, and supposts 8 nobles' households
a king's household needs 1ad per day; it consumes twice as much as a prince's household, and supposts 8 princes' households, 64 nobles' households, 512 merchants' households, 4,096 artisans' households and 32,768 labourers' households.
If they are travelling; increase their costs by 5. Therefore, adventurers probably count as travelling artisans.