There are some AMD GPU chips that might work. But Nvidia is just so much better integrated with TensorFlow and Pytorch and thus the much better hardware.

I equate machine learning to art. You may have great ideas and know-how but at some point you have to buy the material (e.g., good paint, canvas, the better brushes, clay, etc.) to bring your ideas to life.

I know it's frustrating having slow machines when testing models... It really kills the enthusiasm.

I suppose the best thing to do is get into or involved with or work for groups that have the hardware and go from there, or buy new good hardware, or build your own for half price.