wire mesh and window screening frames
If you are going to go the wire mesh route, you might consider buying the whole window screening frame kits available at home depot and the like, in addition to the screen mesh.
They are relatively inexpensive, and you'll just have to buy a few extra bags of plastic corner pieces, along with the screen fitting roller tool. A single kit made for a large window should provide you with enough frame material for several 10 gallon cages. Prices may vary depending on where you shop, but it should cost you somewhere between $20 & $30 for everything you'll need, and you will have material left over for future projects.
They do not take too long to assemble, and while they are not as sturdy as the commercially available screen covers, (they will not hold an adult cat's weight, for one

) both the screen and frames come in multiple colors, (if you are not in a hurry, check the store's online catalogs for colors you can order that are not usually available directly,) and they can look quite nice if you take the time to assemble them carefully and make sure the mesh screen fits flat, which shouldn't be a big problem with a 10 gallon cage. Besides the aforementioned screen fitting tool, the only extra tools you will need are a simple hacksaw to cut the frame material (usually aluminum,) to size, and a measuring tape.
Check out the prices of appropriately sized glass and plexy, if you should also need to hold some humidity in your cages. Glass seems to be fairly cheap compared to plexy at the moment, at least locally, but I have not had need of it, so I could not tell you the best way to obtain it. (I have been able to use regular aquarium covers so far on those tanks I need to hold relatively higher humidity in.)