It took ~ 660 T-145 steel posts to surround my 80 acres. It's a "pure" rectangle - 1320x2640. About 165 of my "posts" were wooden 2x4 angles. Due to bedrock. Slowly but surely - with the help of my neighbor and his commercial jack hammer - all my wooden "posts" have been replaced with T-145 steel posts.
My four wire - barbed wire - fence was, and still is, stretched tight. This allowed the wood "posts" to work pretty well.
These "posts" were simple. A 2x4 flat on the ground. A vertical 2x4 attached to the flat one. A 2x4 running at a 45 degree angle and attached to both the flat and vertical ones.
I would cut all the 2x4's to the correct length - transport them with the tractor. Assemble them - raise the barbed wire, one wire at a time and attach to the wooden "posts".
Many times the neighbors cows would be there to watch. I don't think they ever understood that they were being fenced OUT.
There is a new property owner - right across the county road from my driveway entrance. He came to talk to me the other week. He got an estimate on installation of a four strand barbed wire fence around his 20 acres. He was in a state of shock. I told him he could always due it like I did.
As I remember - all the rolls of barbed wire ( 26 or 28 ) and the 660 T-145 steel posts - cost a total of around $5800. Buy in bulk and save some money.