You can get a rough idea, at least, of this, using Expert Flyer. You can enter a route and a flight date and see all the fares available for it, along with restrictions (21-day purchase, Saturday night stay required, etc.)

This gives you an idea that, at some point with 21+ day notice, a ticket might have been, say, $250, but within the 7-day range could have gone up to $700.

Not sure if it keeps old fares that have been removed, however.