Yes of course prices. I will answer from my own account since mana is still an issue. We do not plan to make stuff available for only one week, but the prices will only be valid for one week. we have talked about how to handle the expenses of making the thing compared to the sometimes volatile nature of steem price, and decided that we could not guarantee a given price for more than the duration of a post. we have no intentions of changing prices significantly unless the steem price changes, but just to make sure we are not caught having to sell at a price where we lose a lot of money, to live up to a price.
If the offer runs out and the item(or items) is/are not sold out, it will be possible to still buy them but the price will have to be renegotiated.