I am developing a database to track the price of a widget on an
auction.  Due to size/speed constraints, I would like to keep the
price history of the widget to between 35 - 50 unit prices seen.  The
price may trend
up or down over time and I would like to reflect this in my median
price.  What is the most effective formula for tracking this median
price.  I have to be concerned about outliers that may skew the data
(intentionally or not).

Once I have aquired my max set of 35.  How do I add new prices without
skewing data and be able to show an upward or downward trend?