I found them at Shop Rite in NJ for $2.69 a pack! The offer is available at least through this Saturday.
The cheapest pins at WDW are almost $7.00 each so I thought $2.69 was a bargain just to get the pins. The batteries expire in 2012 so I will have plenty of time to use them. We usually spend about $30 - $35 each trip buying just 4 pins (2 for each child). For less than $30 I just bought 10 pins that I will give to my kids to trade on our upcoming trip in August. My kids love to trade pins so I bought 30 packs of batteries and pins!! I will give them the rest of the pins to trade over the next couple of trips. It provides lots of entertainment for the kids for a small price, and, as I see it, I got 240 batteries for free.