Consulted my cousin, a horse guy. He builds windbreaks with backyard fence panels, the 8'x6' picket kind, tied or bolted to pipe posts.
So I bought three panels and four galvanized poles. I asked if they could be driven with a T-post driver, and the guy at Lowe's said, "Well, I guess you can, but I wouldn't want to." I told him, well, I wanted to, and so I did. I put the four poles in a square and drove them two feet deep, and then wired three fence panels in a U-shape around them. I will probably go back and screw in the brackets that came with the poles as soon as I can get around to it, to make it even sturdier. And, I have one more fence panel to put on top and cover with tin, to make a roof.
Less than $300 spent, and it's working just fine. The heifers stand in there, cheek to cheek and satisfied.