Today you can learn from the best people in your field at no cost

I especially enjoy books written by practitioners: their books are fun to read, useful, and contain no fluff.

Here are 3 great ones you can get for free:

FastAI deep learning framework by Jeremy Howard
https://github.com/fastai/fastbook

Approaching almost any machine learning problem ebook

Pdf link- https://github.com/abhishekkrthakur/approachingalmost

Bayesian method for hackers
Pdf link
https://github.com/CamDavidsonPilon/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers