Well to start off I’m not advising buying two 3080s. I haven’t seen the benchmarks, and on top of that the 3080 doesn’t support SLI so if you do buy two of them you will need to be using software which can utilize two independent GPUs.

If you’re just wanting to learn machine learning you don’t need anything particularly special. I think you would be happy with GTX 1070. There is also the cloud computing route where you basically rent the gpu from AWS. That will be initially more cost effective than buying your own hardware.

One thing to keep in mind if you do go with the 3080 is the power consumption. Ampere cards are going to be much more power hungry than previous generations, and you will need to budget about 320W just to the graphics card. The recommended power supply for the 3080 is 850W.