@CRquantum
We cannot simply estimate performance differences between CPU and GPU from the prices, but discussing how fast a GPU is against a CPU is simple.
When comparing a GPU having the theoretical peak performance (single-precision floating-point number operations/second, FLOPS) of 1030 GFLOPS and the bandwidth of 148 GB/s and a CPU having the performance of 70 GFLOPS and the bandwidth of 32 GB/s, if the program is memory-bound, the GPU is about five times faster than the CPU. If the program is compute-bound, the GPU is about 15 times faster. Those are the theoretically achievable goals under the same algorithm.
I used to use GPUs from 2008 to 2016. Around 2010 there were many reports like GPUs were 100 times faster than CPUs. But around 2015, there were no longer direct comparisons between GPUs and CPUs. Instead of comparisons, the focus was on how much performance was achieved against the peak performance or bandwidth.
In my case mentioned above post, Intel MKL was not suitable for the algorithm of the compact finite difference method. So I implemented a suitable algorithm on a GPU and achieved such a speedup.