Generally, I use modeling products to get the best results. Now, I'm a pretty "high standards" modeler, so I have to use what all the "Pro's" use to get these ultra-realistic finishes, but a lot of guys don't have that standard, or model more for themselves or for pure relaxation, and so cut corners and save money. No problem there.
However, you have to be both careful and lucky. Years ago I tried just using Baking Soda mixed into my enamel paints to simulate rust degradation on mufflers and tracks. Years later, the baking soda reacted with the paint and oozed a gelainous, oily substance out of the paint, resulting in the ruination of almost a dozen models. It taught me a powerful lesson; unless you're a chemist, and can accurately predict chemical interactions, you are tempting Fate by mixing together materials and chemicals whose interactions may not show up until years later, ruining your collection.
For that matter, I generally recommend to spend the few extra dollars and get set up with some quality product. The peace of mind and better results are well worth it in the long run.