The switch voltage rating is just a maximum.
Most home builders will run their limits on 5v with the BOB providing either optoisolation or buffering.
There are other ways to do it. I personally run mine on twelve volts (I already had that handy in the control box running fans)
This can help with noise issues on normaly closed limits. Most industrial applications run them on 24v.
But I would not worry about that at your stage of building.
In fact most of the blokes I know here in Aus with homebuilt routers are quite happy with no limit switches at all.
Have a look at this ebay seller. They have a range of limit switches.