I just got my PC back, and I need an average price for logs/cobble, and maybe a couple other items that are common and/or easy to get.
Well everyone pretty much buys it from /shop unless they can find it on /ah for cheaper, so I'd stick to prices cheaper than that. The shop is there to set a maximum amount for an item, and few people actually have a shop. If you're planning to make a shop I would suggest having a sign that says something like 'All Prices Guaranteed to be Lower than Shop!' or something. I buy tons of stone and wood from it, I would gladly buy it from you for cheaper.