For the fungus gnat fighters, I got these sticky sheets in the post today and cut them up into traps approximately the same dimension as these Bunnings ones.

Works out to like 8¢/trap (or less) instead of $1.29/trap. Being able to make dozens means you can get way more coverage. Also customised the size to be wider for my larger plants, and want to experiment with different shapes just for fun.

They seem to be working, too, in just a few hours many have already caught gnats.