www.refurbups.com is where I've been getting mine and for clients lately. Not sure if they are 100% best price.
I was taking all the used/dead batteries to Auto Zone for recycling. Now they won't let me drop off more than 2 batteries a week.
I just replaced 10 batteries in a client's office on all of their computers. I think I'll try Home Despot and see if they will take the batteries.
we recycle entire pallets of batteries at Battery Plus, and get some money out of it too.