Check with your local Telco and / or alternative media provider and ask if they can supply an "Alarm Circuit" - this is basically "dark copper" between two points ... and (generally) comparitively cheap versus a T1 or optical media.
If Alarm Circuits are available, next order some "Line Drivers" from someplace like Black Box (http://www.blackbox.com)
. generally speaking, you could drive that span at ~T1 speeds.
If you look at something like Cisco's Long Reach Ethernet (LRE), you could easliy (though not "inexpensively") drive the line to ~100 mbps.
For wireless, you *must* have line of sight (and then some - for the Fresnel Zone) or you get "nuthin'"
If you have LOS (+ fresnel), then it's just a matter of getting the right bridges and antennas.