I am very well aware of the costs of operating an aircraft. However, there are some things you should not skimp on - your life, for example. I don't know the ins and outs of the science of de-icing fluids, but I personally wouldn't use anything other than that the officially approved and tested.
36 years of using the correct stuff means that I am stll walking around. If you use a cheap alternative, who knows what the effects will be?