Hey Greg, since you burried the power with the signal you might have a slight problem with stray EMF. A 0 to 5 volt signal will be a little more robust and possibly cheaper than 4 to 20 miliamps.
This site http://www.aprsworld.com/wind2/
has a 0 to 5 volt wind data logger (that will start your very own weather station for when you build the airstrip! LOL). It is powered by a DC adapter of 7 to 40 volts, you probably have a old phone charger or similar that you could adapt or buy their adapter (a whopping $4!). And now the bad news, the data logger sells for $225
, it uses an SD memory card (like in a camera) and can store tons of data (for looking at system performance while you were away) they offer a 0 to 5 volt sensor kit that goes up to 100 degrees C for $8 (it uses ethernet cable similar to what you buried), you could hook up to 3 temp sensors. They also have a 4 channel expansion card for $75 that could add 4 more sensors!
Their SW is totally documented and can be exported to excel, access or SW of your choosing. You can trend and review the data, plus keep it on your computer for future use.
The only thing I am not sure about is whether you can make the sensor cable longer than the 25 FT they show. That might be a deal breaker (aside from the price! hehe), but they state that the anemometer can be hundreds of feet away so there must be some wayto make it work.
Oh goody another science project!
Just one idea that might be of merit, or maybe way more involved than you wanted to get!