The price varies on distances -- TPACs, TATLs (by memory) tend to be $100-$150 range, transcons $50-$75 and short routes as low as $9
From
> Chicago to Madison: $9
> San Francisco to Las Vegas: $22
> Denver to Seattle: $49
> Washington-Dulles to Paris: $99
> Los Angeles to Tokyo: $119
And important for some the annual option include a single companion on the same PNR. Onetime options do not include a companion.