Using the underlying cost, it is not feasible to create a general purpose parallel processor for cheaper than Nvidia. Especially considering the economies of scale. So you basically need to make a bet on a less general purpose accelerator, as Nvidia loses its economies of scale when you do that.

When you include Nvidia's huge margins, this bet is less risky, but it's still only one that the largest companies can make.

Software alone cannot do it, you need to make a bet on hardware.