the gas cost for you is $15?!
Well, there's a lot of opinions about whether or not it is worth going to prereleases. However, if you're planning on going to Fairfax, Midlothian, and Warrenton BRs, there is an additonal factor.
Fairfax BR is on the 23rd; Midlothian on the 24th; Warrenton on the 30th. RR is released May 20th.
So, if you buy cards on the internet, you will not get them in time for Fairfax and Midlothian unless you put them on UPS next/second day air, or something equivilant. The prereleases will be your best chance to get the most cards for a $25 value. You may get them in time for Warrenton, or you could buy them at a retail place on the 20th, you are gambling that the retail location will have them stocked on the 20th. Either way, you will have sacrificed play time with the cards. I don't know about you, but I find the unnatural selection of choosing powerful cards to proxy test from a list of cards to be worthless because you don't experience all the cards in the set, or only experience the cards you have deemed to be good, and therefore are using a weak foundation for your tests.
As you also have said, there is the trading potential. A lot of people show up for prereleases including people who don't come to league. That is a lot of people in one place, enabling you to find what you are looking for. Not to mention the next flight. You could buy a box online and try trading at league, but you won't have all the people at league who were at the prereleases.
You also get card sleeves (while supplies last). I don't know about how well these trade, but you may be able to trade those for cards if you don't want them.
