For a game I need to adjust a price to the given demand.

There's a shop which sells one item. If lots of people buy the item, the price should increase. If less people buy it, the price should decrease.

How could I achieve this?

This is just a little part of the game so I don't need a perfect solution. Just a very easy solution which does it so that the price is adjusted.

Something like this:

• For every sold item, increase the price by 1,000
• On every day, decrease the price by 1,500 (only one time)
• Don't let the price become negative

Thank you very much in advance!