Mark, as mentioned by SB, the vast majority of hardwood flooring is 3/4" and is prefinished with usually 8-12 coats of aluminum oxide protectant. You could also get many types of hardwood without finishing on them too. From my own experience, I think you might find hardwood flooring actually cheaper than buying raw stock, ymmv....it might have to do with the way taxes are applied to the manufacture of the two products. You can also find hardwood in 3/8" as well, if that works better for you (build up with plywood underneath to meet the right height of your existing floor.
