I like Nikes, too, and I paid just $50 for a pair of 2:40s at Road Runner Sports. You may want to check out their online stock, they ship items very quickly and it's nice to have the store here in Seattle for quick and friendly returns/exchanges. Good luck on your marathon, way to go!!
they have a good standard selection of clothing as well,but sizes tend to go fast due to their location just blocks from Greenlake