Cheapest you can get any version of the M575 locally delivered right now (even without coupon for $69, nice).
Not bad if you're looking for a thumb trackball mouse for your ergonomic desk setup.
This looks like the version that uses Logitech Bolt (not the Unifying Receiver) or Bluetooth LE. Takes 1x AA battery (included).
Love mine, excellent quality and prefer it to a mouse