The cost of fence depends on the size of the land; the cost gets appreciably lesser when the size increases.
The cost also depends on the shape of the farm, a perfect square is least costly (well, since there are no circular farms I ever saw). An odd shape can even double the fence costs.
For a perfect square, approximate cost of barbed wire fence for different sized plots will be:
1 acre: Rs. 50,000/ac
10 acres: Rs. 17,000/ac
20 acres: Rs. 12,000/ac
30 acres: Rs. 10,000/ac
50 acres: Rs. 8,000/acre
100 acres: Rs. 5,500/acre