see reclaimed wood a lot on craigslist. more of here is my shed. you tear it down for me, and you keep the wood of what you want type of deals.
hit searchtempest and put in "lumber", "wood", "shed" as different search results and look at nearby cities of what folks have posted. or look at your local hardware store you generally goto at prices for the lumber.
with above said, i have torn off the old wooden deck, a lot of it was dry rotted. but the pieces still in good shape. built some shelves out of it, to help clean up the clutter of tools. rather heavy duty shelves but *shrugs*
i stopped pulling nails, i just grabbed the reciprocating saw, with a longer blade for metal cutting, and began running it down the sides of the lumber to cut the nails off. that hammer and pry bar got old real quick. i think i may have used circular saw in a few spots on the old deck. just to cut out some good parts and let them drop so i did not have to deal with 10 to 16 foot boards.