In my first response I suggested that if you use gill net, to stretch it it tightly so as to NOT get the hawk entangled. Well, now I think you might want to get him entangled!
Here are a couple of links to companies that sell the monofilament webbing without floats or weights. All you are paying for is webbing. It costs somewhere in the neighborhood of $10.00 a pound or $.38 cents a foot. I can't remember how much you get in a pound. But, the smaller the line is and, the larger the mesh is the more net you get per pound. You obviously want small diameter line to prevent him from seeing it. The mesh is measured in two ways on the chart. The length and width of the square and the measurement of the mesh stretched diagonally.
This company's webbing costs about $10.00 a pound
http://www.louisianasportnets.com/4mono.htm
If you need to talk to someone, they are really fine folks. Remember, lighter line and larger mesh means more net per pound.
Here is a company that sells it by the foot. The mono net that I"d use cost about $.38 cents per foot. ($38.00 per 100ft)
https://fishnetco.com/component/content/article?id=93:monofilament-flag-nets
Here is how I would rig a net to CATCH a hawk. First, you'd have to make the net easy to detach from the pole. Here's how you do it; Run a heavier string from the top of the pole (drill a hole to tie through) down as far as the net is deep. Run the string through the spring hole in a dozen or so clothes pins. Tie a knot around the top clothes pin on each end of the net to prevent the whole thing from slinking down to the ground.
Tie the string off now where the bottom of the net falls lower on your pole (another hole drilled to tie through). Do the same thing on the other end of your net. Now you clip one end of your webbing to the "jaws" of the clothes pins. Do the same on the other pole.
You won't be able to stretch it tightly because the net will pull out of the jaws of the clothes pins if you have too much tension.
When the hawk hits the net, the net will fold around him, and the net will pull free from the clothes pins and drop like a sack-a-patatas!
You would probably be able to get several folks here to sorta "rent" the rig from you, to help with the costs. Like I say here at times. It wouldn't take long to pay for itself when you consider the cost of the chicks, feed, meds and time spent raising them.
