I don't know whether it was in this group, or another, that someone asked about a solar-powered remote temperature sensor.
I just purchased a Weather Channel "Wireless Temperature Station" from La Crosse. The main unit is your usual atomic clock with an LCD display. A remote temperature sensor is included, powered by a battery recharged by a solar panel.
The unit came from Mac Mall, and cost all of $16. (I'm currently a member of some shopping club and got two-day FedEx shipping for free.)
I don't know how good it is, but you might want to look at it.