Mine were pretty easily made. I laid the bottom two dropboards (mk 1 boat) on a piece of plywood, traced and cut them out. Then I cut out the center of the new boards leaving 1.5" around the perimeter. Then I sanded and varnished them, and stapled mosquito netting to the inside. I even used fancy SST staples that I had lying around (oooh). Total coast was close to zero.

By doing just the bottom two boards, I still put the top board in place and I can lock the boat up with the nets on if I want to leave it while locked up on hot days and go in to town.

If you don't like seeing the staples inside, you could also make the boards out of two half thicknesses and trap the netting in between. Just depends on what size of plywood you have lying around.

My dock neighbor bought a screen kit from the home store and formed them to fit the companionway. Came out pretty nice and very quick to put in place. He made a panel for the top that lays into the hatch tray too. It just matches up to the vertical piece.
Our screen is a velcro on type with a zipper down the middle that is pretty convenient but I keep catching stuff on it as I go through so it comes down at the wrong times when coming and going from the boat.