If you have a credit card with a "normal" ceiling you probably can rent enough on neocloud providers like HuggingFace or Mistral Forge.

I'm not saying it's worth it but you don't need to buy a GPU yourself to be able to train.

This is the whole point of Karpathy's nanochat which OP refers to, to train a GPT-2 level LLM for under $100, renting an 8xH100 VM.