Determine the surface area to be blasted. A relatively limited area, such as a car body, will, of course, cost less to soda blast than a large expanse like the facade of a multistory building.
Calculate how much it will cost to rent the equipment, if you don't already own it. For most jobs, you'll need a soda blaster with a compressor of at least 185 cubic feet per minute and 150 pounds per square inch.
Calculate the clean-up costs involved. You'll need to dispose of residual bicarbonate-of-soda. One of the advantages of soda blasting is that the material is water soluble, making it easy to wash away, but you'll need to calculate the cost of water usage.
Factor in residual costs, such as the expense of protective gear. You'll need to wear a face mask and protective gloves and goggles while soda blasting.