As a teenager I had a pretty good sense of how much things cost. One of my chores as a preteen/teenager was to write out the bills each month. So I would write out the checks (minus the signature), log what had been paid on the spreadsheet, and file the bills. My parents had me do that so I could understand how much things cost and how to handle finances. They of course checked my work to make sure everything was done correctly. so by the time I went to college I had a pretty good sense of how much things cost (at least in Southern California where I grew up).