You take a big risk doing what you are asking. Think about it this way, if you do get scammed then you are out the cost of two CPU's. Then, suddenly that $50 doesn't seem like much.
I am not insinuating you are going to get scammed, but hey, it's the internet.
I don't live near a microcenter, but if you go this route and find someone you trust, they usually offer discounts on motherboards with the purchase of a intel CPU (might only be SB).