I want to posit a thought for you all:
Those of us in a modern day society often forget what the world was like before mass production of goods and services.
What was store markup like for purchase of items 150 years ago? 500 years ago? Markup on items for reasons ranging from supply and demand to storage problems ranged from 100 to 200%. This trend is today still carried on in middle eastern cities and towns; the ability to haggle and barter is part of a cultural heritage in a premodern society.
Life before Sears and Roebuck was quite different, and this difference should be given thought before setting prices.
In my campaigns, I always have the two hagglers compare diplomacy checks to gauge prices, and allow them to take 10 if they wish. Every point of difference between the rolls equates to about a 2% price difference, rounded off for ease of use. I don't tell what kind of a discount the palyers get, just like the fact that shopkeepers don't normally tell their customers how much of a discount they are getting from the cost. It's haggling, and it forces the players to have their characters get good on their negotiation skills, or get stiffed.