Fiber and media converters are suitably cheap. You can get the TP-LINK MC220-L for around $20-30, and the optic for as low as $35 depending on your source and type/distance. This works well as you don't have to worry about shielded cabling if you ran something like cat5/6. You can also reach much further distances than with copper wire. You don't necessarily need permits, but you do need to call MISS-DIG, or whatever the local version of that is. When the guy comes out, tell him exactly what you are planning on doing, route, possible routes, etc. Most places require a hand dig within a few feet of any marked utility. The rest you can use a rented trencher to do. Running conduit will make a lot of sense, you typically need schedule-80 which you won't find at lowes/home depot. You can also call a contractor to do this work, depending on the distance it may only cost a few thousand dollars at most. If your goal is to keep things super-low cost, then wifi or other networking may be your ideal solution. Look at the hardware from ubnt.com and see what works. If you don't have line of sight, you will need to run a cable to make this work. If cost doesn't come into the equation, you can also get SFP+ PCIe cards and do this at 10Gb/s vs 1Gb/s much easier. Make sure you run single model fiber, otherwise you may have troubles if you encounter older OM1/OM2 and try to launch 10G signals.
Hope it works out!