Does anyone know how much Adobe charge for a 3rd activation for a copy of CS3? We have it on our laptop, desktop & have just bought a new desktop and it won't let me activate it unless I deactivate one of the other computers or buy a new serial number and I was curious to know how much it costs but I can't find a price on their site anywhere.

You'll need to purchase another full license to install it on the 3rd machine.