Are there any free APIs that allow you to generate high frequency historical datasets?

I tried to do some research on this and I eventually ended up in contact with barchart, but then they want $500 per month for a historical data API even though one of the tutorials online said that I could get access for free. I'm trying to do training on a ML model, so I need at least a million rows to generate good results. Even a csv file with high frequency data would be great. All csv's I've looked at don't have anything less than hourly though.