Just replaced my LX passenger side, $178 out the door from the dealer. Two bungees on the bottom, pop out the footwell light, two screws tucked up under the bottom edge of the pocket, and then pull down.
I've noticed some dealers use a 3rd party warehouse for parts with much cheaper prices than Lexus fulfillment. Check your local dealers if their online parts catalogue matches the same format then call and ask if their parts counter can match their online pricing. An example would be Longo Lexus or Keyes Lexus out here in SoCal. Their online parts service matches the discountpartsmonster website with very close pricing and you'll save shipping.
PO for black pass seat back (71705-60300-C0)