Parts - buy/sell to help fellow members or make $?

I try to help others out with parts, at a very reasonable price. My "toy" budget is very small, and I know there are others in the same boat. Many have helped me with parts at a price (many free) I can afford, and I try to do the same. However, I do need to make a small profit on some parts, so I can buy what I need. I got a deal on a "A" body 8 3/4 rear. If I were to sell it, I would sure ask more then the $200, I paid for it. But I sure wouldn't ask the $800 up prices I see some asking.