cheap flights to usa

[myst311]

I graduate on 30th June and want to go travelling on the West Coast of USA more or less straight after. The thing is I'm skint! I was just wondering what's the cheapest way of getting over there?? Heard rumours that you can turn up at an airport, wait there until a free seat arises and then buy it on the cheap... is that true??

I've looked at flight prices online but you have to type in departure and return dates, that doesn't apply to me as I can leave anytime.

Any help would be gratefully received!