Fantasy stock/shares trading

G'day there, I'm looking for a script that will allow me to create a virtual trading centre. It will be like a game. I will use 1-on-1 basketball for the example here, although it won't be the situation i will really be using. Users will need to register and they will start off with 5000 credits to purchase shares in a particular character. The characters will then go 1-on-1 with another character. After the game has finished, the winning characters' shares will go up, and the losers' share price will go down. This will calculate for the user and give them credit. Users will be able to buy more shares with their winning credits. They can also put their shares up for a certain value at their own choice. Buyers can also make an offer for any share they want. It would be up to the seller/buyer whether they choose to sell/buy. I haven't decided if I would rather a linux/php/my sql database or a windows/asp/mssql database for this yet. I guess it will depend on the costing. I only want something really basic if possible?! Otherwise quote whatever you think it will cost...