Summer pop festivals aren't always the bargain they seem, but some would be a bargain under any circumstance. Take, for example, today's WHFS-tival at the Prince Georges Equestrian Center in Upper Marlboro. Not only are the bands great -- the lineup includes such new music comers as the Soup Dragons, the Charlatans UK, They Might Be Giants, the Ocean Blue, the Wolfgang Press and Catherine Wheel -- but the $7 ticket price (only $6 if you bought early) makes it the bargain of the season. The gates open at 8 this morning, and the music starts at 11 a.m.; the predicted finish is 9 p.m. Call (301) 952-4740.