Erm...for this mod you will have to do similar things as one would have to do for getting transparent side panel.
For your mod you have to go through following process:
I. Preparations
II. Cutting and drilling
III. Finishing
IV. Fan and grill installation
I. Preparations
You need to make marking on your cabinet for the cut out. Identify the fan size and positioning of your fans and mark accordingly. Before cutting, make sure that you cover the cabinet with masking tape(non stick, writable) and mark the area you are going to cut. If masking tape is not available, you can use pencil on metal sheet directly(not recommended).
II. Cutting and drilling
Cutting:
Dermel tool is the best option for cutting, if you own one, you know what to do. If you are not too sure about cutting process, you can ask for help at any cabinet/carpentry workshop.
On cheap you can use options like:
- Wire cutter- Assuming your cabinet's sheet is not too thick, you can cut the sheet using simple wire cutter. Anyway cheap cabinet these days are made of very thin material.
- Chisel and hammer- Chisel and hammer can be used for cutting. While using chisel and hammer you will have to lay portion to be cut on ground, so take care not to hit other parts of the cabinet and put thick layer of paper below cabinet for extra protection of cabinet and floor. I had asked for help from cabinet workshop guys in cutting my cabinet's side panel, while I was working on my case mod. They used chisel and hammer for cutting. It took just two minutes and their trained hand gave the side panel quite good finish.
Drilling:
Drill the holes according to marking for your fan screws.
If you are getting help from any workshop for cutting, get drilling done from them.
Hand drill with metal cutting bit(whaterver it's named) can be used to drill on sheet too(Have tested personally

).
III. Finishing
If you use masking tape, half of your job is done. It's very much possible that uneven edges are left after cutting. You can use 'U channel rubber'/ 'U channel rubber'( called as "goat" in Marathi) to cover the edge. U channel rubber is used for covering edges in scotter, you can get it from automobile spare parts shop.
IV. Fan and Grill installation
- You can get fan grill from local computer shops, they don't cost much.
- Make sure you add some rubber material/ rubber gormet while installation to avoid any vibrations.
If you are going to do this mod and you also wish to get transparent side panel, get it done along with this mod. Process will be similar. You will have bigger cutout(easier to work with), and will need to buy acrylic(acrylic not glass) side panel. Velcro/ screws maybe used to fix acrylic sheet to side panel.