The Glamis store sells the weekly permit for $50 and the yearly for $150. Same as the Ranger Station on Gecko Road.
Last I heard the gas station in Palo Verde on the 78 between Blythe and Glamis sells the weekly for $35.
Call ahead to wherever you plan on getting them. It is my understanding that they make the vendor's pay upfront for the passes and at this time of the year nobody wants to buy passes that they will not recover the cost of. With only four weeks left of needing them nobody in there right mind would layout any money to get more of them.
Had trouble finding them at usual stops from LA area last week. Got them at Pilot travel center at 111 & 78 in Brawley. It was the fourth or fifth stop looking. Good Luck!
This year has been tougher to find weekly passes, at least for our group. This is the reason I buy a season passes every year, I hate stopping to buy a season pass. Another 15 minutes saved for the sand.