The problem is whether they're reliably the same. A 10 cent bolt might one day be stronger than you expect, and that will cost you a lot more than the $4 extra for the proper designed one.It would be interesting to take a factory shear bolt, and several cheap bolts from the local hardware store. Test the shear breaking point.
I'm guessing a grade 3 bolt at 10 cents apiece is about the same as a factory shear bolt at 4 dollars.