To some extent, you get what you pay for. In hairspray, you can pay a lot for a well-recognized name or for a fragrance that smells nice. For an art spray fixative, you are paying for even dispersion of the spray and a good acrylate coating that will preserve your piece.
Some hairsprays will have the same ingredients as art fixatives, but be wary of the dispersal system (spray). There may be some excellent hairsprays that will serve your purpose. They may or may not cost less than the art spray.
Also, be forewarned that many hairsprays contain hair conditioners, which is usually another name for a natural or synthetic oil. These conditioners could leave grease spots on your art. The oils to avoid are dimethicone, silicone (anyone pretty much), anything 'oil' or 'lubricant', vitamin A or E (both are oil-based), anything ending with 'glycol'. Be wary of anything listed as a plant extract.
I would think the really inexpensive, no-frills sprays might work well, like maybe White Rain or Final Net or some other hairspray that has been around for several years. Just look for an acrylate in the ingredients. Suspension in alcohol is probably better than in water.
The quality of the chemical isn't any higher in art spray. The concentration might be higher, but I think extra-stiff hairspray would have at least as much. The nozzle or sprayer may be better on the art spray and the formula may have been mixed to deliver an especially fine mist.