Slice up the Money Pie. The new price for each weapon is based on the total amount of money spent on that weapon. The percentage of money spent on each weapon during the week is used to determine the percentage by which its price moves the next week. So if 10% of all dollars world-wide are spent on the Maverick M4A1 Carbine, then its price will increase by 10%.
Take notice folks, the doomsday approaches. Valve has announced the big changes in the economic system of Counter-Strike: Source. And it's a doozy of a change. On October 11th, the world will come to an end, and millions upon millions of cranky boozed up gamers will go insane and riot in the streets. OK, maybe not that bad, but I can see alot of "interesting" threads being posted on the Steam forums that's for sure. I won't bother explaining things, I'll just paste it in here for all of you to read. I will post some of it here to start, just go into the extended area for the rest, enjoy.
Most of the weapons and equipment in Counter-Strike have had the same prices since the day the game was first released. These prices greatly affect the overall balance of the game. We at Valve know we're not alone in thinking that some of the prices in the game have never been exactly what they should be. (Uh, night-vision?) But rather than tweaking the values ourselves, we thought we'd rather let you decide. Coming soon in Counter-Strike: Source is a new system that sets the prices of what you can buy based on, well, what people are buying.
Starting on October 11th, the prices of weapons and equipment in Counter-Strike: Source will be updated each week based on the global market demand for each item. As more people purchase a certain weapon, the price for that weapon will rise and other weapons will become less expensive.
Gather player purchase data. Each week, the total number of weapons purchased world-wide since the previous week's change is counted. The purchase data is gathered directly from game servers. Every 24 hours, game servers upload a file to Steam listing the quantities of all items purchased over the course of the previous day.
News source: Steam Counter Strike Weapons "Market"
Link: Steam Forums Thread