I like using Iron-X, TRIX, or 3D BDX (Slightly cheaper) for chemical decontamination. I use a diluted Optimum Power Clean as well on a certain super super nasty car (This will be very harsh though). I don`t think we need a degreaser as I feel that soap is enough to break up every dirt in the car besides tough iron particles or tars. Occasionally, some cars got stained with tree saps that I use GooGone and plastic blade to remove it for a cost efficient method.
The method I use for cleaning customers` cars starts with pre-rinsing to move out the dirt first. Spray OPC into tires and wheels, wait for 1-2 mins while agitate it with a low-profile tire brush & mother`s wheel brush / speed master wheel brush. Rinse it with water again. Then, I start to check around fenders or lower part of the vehicle and spray some iron-x stuffs to help break up the brake dusts that stick on the paint and wheels. Let it sit for 2-3 minutes then rinse it again. Wash the car with a good soap and give it a good rinse. Then, NanoSkin or clay bars come into play as the last step!
I only use degreaser on engine bays. This is my method for decontaminating, some other members might have a better method though
Here`s several cost-efficient products that you should have IMHO:
Optimum Power Clean -> Great for tires, wheels, and nasty stains (I don`t usually have to use iron-x on wheels after I use this product). Try to buy the gallon size and dilute it 1:3
3D BDX -> One of the most cost effective iron-x like products that can be used on wheels/paints as well based on the demo video. Some members found the iron-x is more effective though, but I found it to be very very cost effective for using this product instead.
I hope that my opinion here helps
