I bought a bugbuster screen for our forward hatch five seasons ago. It wasn't cheap, but is still in great condition- no tears, no split stitches, and it has seen a lot of use and UV exposure. It installed as soon as the boat goes in the water, every season, so it is in place from May to October in all weather.
SOGEMAN BUGBUSTER 12" X 18" INSECT SCREEN -HATCH The Chandlery Online
Knowing what I know how, I would stitch one up myself, using sinkers as ballast to keep the foot snug to cabin top.
Baggy screesn like this have a real advantage over fixed screens covering the hatch from the inside, in that you can poke your head out through the hatch without having to remove the screen.. which is nice when climbing into a low-overhead v-berth.