Have you considered not buying a GPU at all and making using of paid services from Google Colab, lambdacloud, etc.

You can use these while you learn, and learn more about your requirements, and make a more educated decision later.

Colab free tier works great for short experiments, and next up tier is just 10$ a month.

AMD is also set to announce new GPUs on November 3, depending on their price all last gen prices should go down.