I won't go into it on a pure maths basis but basically a player's price is always in a state of flux. It waxes and wanes based on the number of points a player makes in any given round. It then plots itself on a curve and is averaged over 3 weeks (although there is minor carry on stretching back further from what I can tell).
So if a player has a break even of 50 points, it means that he needs to score 50 points for his price to remain the same. Any less, his price goes down. Any more, his price goes up.
But that particular week's score will have an impact not just on that week, but for numerous weeks. So if he scores 100 in that week his price will jump up a lot immediately and his break even will drop a lot. So unless he plays like a complete tard you would expect him to increase for 2/3 weeks thereafter.