I've tried various synthetics and wool, including the Ex Officios, and have tried running shorts with built in liners... and after everything I've tried, I am most comfortable in Icebreaker Beast, relaxed fit boxer briefs... They list for ~$45, but I've been able to find them for ~$20 -- they've got some up now on Sierra Trading Post in the mid 20s, but STP always has so many coupons, you ought to be able to bring that down.
They work great for days of hiking. They do dry a lot more slowly than synthetics, so you have to keep that in mind if you'll be swimming in them (which I've done several times), but at 2.7oz (size small), for those of us that are just aiming for "lightweight" and not UL or SUL for right now, taking along an extra pair isn't a hassle, and the odor-resistance and comfort easily make it worth it, IMHO.
Underwear is something that is worth splurging on IMHO -- keep the important bits well taken care of, eliminate chaffing, odor, etc... hard to put a price on that.
As a second consideration, the Ex Officio Give-N-Go line of synthetics comes in a close second for me and is about 30% cheaper, with much faster dry-times.
As a counterpoint, I've tried some of the Ibex line (wool like the Icebreaker), and the Icebreaker is far, far superior for hiking comfort.