I can either start mining with it right away and keep it or sell for $250 unused which will allow me to buy another one.
But, if I sell I will have to wait for shipping and will miss out on the profits I could have generated in that time.
And, it would be at least a good week before I would receive a new one that I bought online (if I can even find one at the same price, free shipping is nice).
He doesn't have to buy it if he doesn't want to. Shipping to Brazil via USPS priority mail was about $44 when I checked. Then, factor in the cost of gas for driving to and from the post office, and the actual amount of time doing it (which is valuable to me in its own right), and I only stand to make about $20-55 off the thing, depending on how you look at it.
Offer is on the table, and it is within the price range that he proposed.