I swung into the Petaluma GameStop the other day to pick up a backup copy of “Culdcept Saga” they had on hold for me. (I’ve taken my copy in and out of the DVD case so many times it’s started to crack a bit near the spindle, can you believe it? I figured it was best to grab another while the game can still be had for $20.) While I was there, I decided to pick up Wii MotionPlus, the new Wii accessory that allows for more realistic motion tracking in games. A copy of “Wii Sports Resort” (rated E, $50, out Sunday) arrived on my desk last week. It comes bundled with one Wii MotionPlus, but if I want to play the game with my wife or a friend, I’d need an additional MotionPlus.

Wii MotionPlus is supposed to sell for $20, but GameStop charged me $25. Unfortunately, because I was in a hurry, battling a head cold and was buying more than one thing, I didn’t realize I’d paid higher than the suggested retail price until I was sitting at my desk in Santa Rosa. Then I remembered reading a couple of months ago, when GameStop first started taking preorders for MotionPlus, that they were charging more than everyone else for the peripheral. At the time, I kind of shrugged my shoulders, figured the screaming Internet hordes would generate a flood of complaints, and the price would come down by the time I actually bought one.

Well, I was wrong. GameStop is still charging a 20 percent premium for the accessory. I checked the websites for a handful of other large retailers that sell video games — Best Buy, Wal-Mart, Target and Amazon — and they’re all selling Wii MotionPlus for around $20. (I couldn’t find a listing for the standalone device at Game Crazy’s site.) So don’t make the same mistake I did. If you’ve preordered “Wii Sports Resort” from GameStop, pick up that extra MotionPlus somewhere else.

I suppose I should say somewhere that I have no beef with GameStop otherwise. I shop there quite frequently. And the Petaluma store seems merely to be following corporate policy. (Wii MotionPlus is also $25 at gamestop.com.) But why pay $25 when you can only pay $20.