Best method for medium range, low data rate communication?

I want to connect 3 seperate buildings in a rural setting to share some
sensor readings, and possibly provide some control between them.
Maximum distance would be 1.25 miles. There is telephone at one
building, but I don't want to install it at the other 2. I would
prefer my own private digital link.

What are my options, buried cable or fibre optic, wireless? Cost is a
factor also as I don't want to remortgage the farm to do it.

.