FL Cracker
For 1 wire electric, I place the wire at 30". If I were building a 2 wire, probably 34" & 18". IMO-1 wire is adquate for cross fence & it allows small calves to creep graze the greener grass across the fence.
Key items:
1. Powerful charger-6 joule output minimum
2. Adequate grounding-use at least 3-6 ft ground rods.
3. Electric fence training area. At my home place, there was a 1/4 acre trap with a five wire barbed wire fence. I added an offset hot wire to make a training area. On another place I built a trap with a 4 wire high-tensile electric with an electric offset wire. By having the hot wire backed up with a visible multiwire fence, most animals will not run into the fence but approach it slowly. Some of the offset wire is steel, some poly tape & some polywire. This gives the animals exposure to all kinds of hot wire. Poly tape is the most visible & flutters with a breeze. Also you can tie small strips of aluminum foil to the wire for more visibility. These training areas are attached to my corrals. After unloading into the corral, I open the gate into the training area and walk away, not pushing them out. By letting the cattle go out on their on they usually walk or trot slowly & check out the hot wire by sniffing with their nose. One zap on the nose and they are usually trained. If possible, I like to leave the animals in the training area for at least 12 hours overnite, but have turned out after 2-3 hours when rushed for time.
As far as cost, 1 wire 14 ga soft steel wire with 3/8 in fiberglass line post and steel t post or 5/8 in fg corner post would cost about $.05/ft for materials, the 2nd wire would cost less than $.02/ft. Don't have a clue on labor cost as I build them myself. Until I'm sure I have the correct layout, I use poliwire, after 2-3 yrs I will replace with steel. Goes up pretty fast compared to barbed wire. I don't use high tensile for cross fences, only for perimeter or training area fences. High tensile is very stiff and some what difficult to work with.
The link below has a free catalog with good fence building tips. A very good company to do business with & price competitive.
http://www.kencove.com/
Hope this is helpful. Just my 2 cents worth.
Good luck & happy trails.
Brock