A supercomputer might cost $200M and use $6M of electricity per year.

Amortizing the supercomputer over 5 years, a 12 hour job on that supercomputer may cost $63k.

If you want it cheaper, your choices are:

A) run on the supercomputer as-is, and get your answer in 12 hours (+ scheduling time based on priority)

B) run on a cheaper computer for longer-- an already-amortized supercomputer, or non-supercomputing resources (pay calendar time to save cost)

C) try to optimize the code (pay human time and calendar time to save cost) -- how much you benefit depends upon labor cost, performance uplift, and how much calendar time matters.

Not all kinds of problems get much uplift from CUDA, anyways.