Airfares!! I just dont get it

[DavidMn]

So anyway, I'm going out to Washington D.C in April for a few days to see a couple baseball games at the new ballpark that's opening there this year. I looked up online for airline tickets, and for the dates I was looking for, National Airport was $525 RT on Northwest. So I did a little snooping and looked up the same RT from Minneapolis to D.C but this time to Dulles. know what? $201 RT!!!! And I found out they have city bus service running right from Dulles straight into downtown D.C, so it's only a minor inconvience. I know there are things like availability and what not that determine the cost of a ticket, but 300 F***IN dollars? Anyone else have a similar experience?