Looking for an inexpensive button that can withstand hits from a baseball bat
Two pieces of metal separated by small slices of foam rubber at the corners make a cheap and simple heavy-duty pressure switch. Attach wires to the metal and you're good to go. Copper flashing from the hardware store would work, but might not last long enough.

The next problem is how to get the data into the PC. There are any number of ways to do this, but the simplest is by connecting the switch to the data control lines on a PC serial port. By reading the state of the flow control lines you can determine whether the switch is on or off. Don't have a serial port? A USB to serial converter will take care of that.

This link has an example of how to connect the switch and read it.