Fiber the Way to Go....
If you are going to go to the trouble of 'putting a hose in the ground,' fill it with optical fiber!
Ask around and see if you can find anybody deploying fiber, the phone company, cable company, utilities, etc. (Search the local news?)
Most of the time, you can get 'scraps' of large spools left-overs for the price of just asking. They won't be using much of anything less than 100m or so, and you might get lucky and even find a chunk that is 200m or so. Connectors can be purchased that don't require expensive polishing kits, and again, maybe who ever is giving you the scrap might let you use the installation tools if you buy the connectors! The media converters (as mentioned earlier,) can be obtained from Ebay. Probably the connectors as well. If you are lucky enough to get direct burial cable, so much the better. (A bit messy, due to the silicone gels though.)
Perhaps an ADSL modem set ('cable extenders') may also fit the bill if you want to stick with copper.
1.6km @ 16.6mb/s over 24 gauge phone wire, although it's expensive...
Also look for 'long reach ethernet' gear on ebay or elsewhere.
If you are going to stick with microwave, look at these calculators:
Also, at 5.8 gig, reflectors are a real possibility if you, (or at the other end,) happen to have a neighbor that DOES have line of sight to the other end of your path.
Search for passive microwave repeaters.
If the reflector is close to either antenna, they can be fairly small.
I know of several people that have built 'fly swatter' type reflectors so the electronics are down on the ground, and the reflector is the only thing up in the air.
In the middle of the path, the reflectors get pretty big, (think BIG BILLBOARD,) so putting one up on the side of a building or barn may or may not work for you!