why do taxi drivers cost money?

Do you work for free?

Id imagine they have expenses like fuel, vehicle wear and tear and their time

Shrek, taxi drivers are service providers, whether independent or hired by a company; they provide a service and require payment in order to profit.

Is gas free? Car repairs?

Huh?

Taxi drivers don't "cost" money. They either "require payment for a ride" or they "spend" money.

Grammar matters

would you work for nothing

You do realize that taxis are cars which use gasoline (usually) and require maintenance all of which cost money. Also, the drivers have to make a living.

because they need to eat and keep a car running

They have three eggs and a police van.

Nobody works for free