This is not an issue. If someone wants to sell you 1 of an item then they shall do so in their bazaar of their own choosing. Pricing for one item would naturally be higher than the price per item from a stack. Thus if you could just nickle and dime people's stacks of items they'd just have to raise the price of the entire stack to compensate. Some people will sell smaller amounts of materials to get a higher profit per material. I think you should look at just paying that price if you absolutely don't want another 90 of some item but don't want to gather it either.