Low cost limit switch suggestions

Hi,
I'm putting servos w/gekko 320s on the x and y axes of a
older ball screw equipped mill and am going to use CNC PRO.

In talking to Mariss of gekkodrives he recommended that the
limits kill the power to the drives because if a drive fails
there is a good chance that the output transistors will
short and the motor will travel at top speed until it blows
the fuse or hits the end of the ballscrew (not good).

This means I used up the original limits that are on the
machine.

So here are the questions, does any one have a suggestion
for limit switches that are inexpensive, rugged, accurate,
and relatively small (I want it all). Also it would be nice
if I could only have to install one per axis which brings up
the second question,

If I already have max. travel limits do I need any thing but
a home switch?

What are the reasons for having limits the computer can see?

Bob KB1FRW