You need about 200 bucks.
Thats what they cost when I was looking.
Its a plastic type film you apply over the monitor. ( actualy 2 layers of plastic seperated by small spacers) when you press on it, you make a connection between the two peices of plastic, that sends a signal to the controler, and the mouse moves. they plug in to the mouse port, or serial port.
I couldnt find any of my old links, but they are sold seprately.
Depending on your screen and it's size, there may be a solution for you at www.elotouch.com - that is where I found the perfect fit for my 6.4" LCD. There are detailed instructions there on how to add it to your screen. It isn't rocket science, but it isn't exactly easy either. There are many other companies that offer "add on kits" as well.