It varies widely among airlines, the last time I booked United for SFO->SEA (a 2 hour flight), they wanted $89 for "economy plus" and ~4 inches more legroom. And even with the extra legroom, the seats are still quite narrow and I have a hard time using a 15" laptop and still keeping my elbows within my armrests.
I think I paid $29 for the upgrade on Alaska Airlines (though you need to do your research, since depending on the plane (Alaska, former virgin, Horizon), you may not get more legroom, just a seat closer to the front and maybe a free cocktail.
I think I paid $29 for the upgrade on Alaska Airlines (though you need to do your research, since depending on the plane (Alaska, former virgin, Horizon), you may not get more legroom, just a seat closer to the front and maybe a free cocktail.