It's almost impossible to charge $1 for something. As soon as you start charging you need, a secure site, a credit card processor, accountants, lawyers, tax accountants, tax lawyers - repeat for each state/province/country/jurisdiction.

You go from a company with a dozen programmers enjoying what you do to a company of 1000s of employees making sure you have met the requirements for an out of state advertiser in Nowheresville Ak