Wire mesh has proven to be a difficult commodity for me to find locally and at a decent price. I was able to discover 2 meshes made by AMACO, a craft company, for under $6.50 each.
http://www.amaco.com/prod-wireform-metal-mesh-368.html The first, which I have yet too use, is silver in color and has a diamond grid pattern. The second is black and has a simple square grid. Both meshes are 100% aluminum and measure 16" by 20" unfolded. I used a portion of the black mesh for creating a mesh window in my old dell case.The mesh comes in a small package wich requires a single lengthwise fold and 3 widthwise folds. The mesh must be pulled out of the package and carefully unfolded as to not damage it. Despite extreme carefullness on my part, the black coating fell off along some seems. This did not pose a problem for my mod, and could probably be fixed by painting the mesh, but it is still a nuisance.
Some pictures of the packaging and mesh.
After successfully flattening the mesh I laid it over the hole I had prepared earlier for the mod. I was able to bend the mesh slightly to lay a portion of it over the hole. The next several minutes were spent deciding how to best mark the mesh. While a fault of mine and not AMACO, some suggestions on the package on how to work with the material would have been nice. I suppose a white crayon would have worked. I ended up grabing a role of masking tape and laying on strips showing where to cut. As I cut I was able to bend back the extra mesh and keep it out of the way.

Once I cut the panel of mesh to the correct sise I needed to make a number of smaller holes inside of it in order to clear projections on the case side. The yellow sheet metal cutters I had used earlier worked fine along the outside, but were cumbersome for finer work. For this I used a small, sharp pocket knife. By supporting the mesh on one side and pressing down with the knife on the other side I managed to make cuts easily and without cutting myself once. In this way I outperformed myself, as normally I cut myself at least once, or failing that I am bit by some metal protrusion in a case that is never located. The mesh started to show its ugly side with the cutting however. In spots the weak connection between perpundicular wires would fail, leaving a raged pattern that is rather unsightly. The masking tape from earlier became helpful. The mesh could be both prevented from fraying further and reinforced along vulnerable edges already cut. The meshes weakness was usefull when trying to push through screws sligtly biger than the holes, as the mesh would give sideways slightly. Also some of the smaller protusions on the back of the case could snap through the mesh if sufficient pressure was applied. These snapped holes would then hold the mesh to the protrusions quite effectively.
(I am sorry about my leg in the following picture, but I needed to support the thing and take a picture all at once.)

After maybe 15 or 20 minutes of work I had the mesh in the window and 1 120mm thermaltake fan mounted. The hole allowed the fan to be mounted easily and without mistake. No more missdrilled holes The airflow through the mesh is nearly unhampered and not any noiseir than without mesh. I used some found bolts and washers to partially secure it to the case side. When more holes are drilled I will be able to beter secure it. I am unable to run my system closed due to clearance between the Cpu fan and power supply but the mesh did seem to help the graphics card tempurature. The card is passive cooled and the fins on it can become nearly burning hot but the airlfow from the fan pushed air past and out of the mesh, Any poor performance here is a result of my own bad planning.

My impression of the product is fairly good and I will most likely use it again. My only complaints are the difficulty in finding it (Even in a store it can be between two or more places), unfolding it, and the failure of the bonds between the wires. It also cost less than modder's mesh which is a plus for me. I would rate the product at a 4 out of 5.