From the Detroit News Online: Latest versions of robotic lawnmowers are pretty sharp
Once it is programmed, this is a tool that mows your lawn for the entire season requiring no involvement by you. It cuts the grass from 0.8 to 2.7 inches high and has mulching type blades so the finely cut clippings add the equivalent of one application of fertilizer to the lawn over the season. The blade is sharp on both sides, so can be rotated at the end of the season for a second year of sharp cutting. A new blade costs about $10.
The Evolution runs on lithium batteries. After working for about four hours, it heads back to its own little house for a recharge which takes about two hours. This shiny red turtle with wheels is so smart, it will go straight to its little house whenever it starts to rain. It is very quiet running and can do hills up a grade up to 27 degrees with no problem. If someone is dumb enough to try to pick it up when it is operating, this little robot turns itself off immediately. If someone wants to steal it, crooks will learn that unless they have the numerical code you used to set it up, the machine is worthless to them.
This little robot can handle the mowing needs of up to 30,000 square feet or 3/4 of an acre. You can program the machine to mow every day, or every other day, or if you can believe this, when the grass is tall enough to need mowing. It can actually detect when grass is taller than its programmed height and sets about cutting all the grass that is too tall.
$2500 isn't really jaw-droppingly unreasonable, either.