Depends on what type of fence you want - barbed wire about $1.50/LF, woven wire about $2-3/LF, split rail or Kentucky 3-board horse fence can be as low as $10-15/LF with pine or similar cheap stake fence can run in similar range, typical cedar or chain link fence $14-22/LF, Aluminum $15-25, Vinyl $24-30, Wrought Iron $45-100/LF installed.
Very roughly, materials is about 40% of the cost on cheaper materials like pine or chain link, 50-60% on most of rest, 60-75% on high-end metal or wrought iron fencing.
For staining or sealing of wood fences add about $0.75-1.25/SF being coated (decide if 1 or 2 sided staining or sealing).
Realize these are rough numbers, and depend a lot on how common the fence material you choose is in your area, and also on ground conditions - bouldery ground, caliche hardpan, or bedrock make the cost skyrocket to as much as double or triple the price because a track or truck-mounted drill rig may have to be used for the holes. Slope and access also makes a lot of difference, as this limits use of power equipment, and of course the effort needed to get concrete to the post holes.
If you are talking 1/2 acre, that is a LOT of holes - you are going to want to rent a power auger (takes 2 grownups or large teenagers to use) for the holes - more than about 10-15 post holes gets to be a real drag by hand unless this is going to be your summer and fall exercise program at one or two a day.
