I know nowadays you can find PDFs of dharma books for free (although not so legally) from google.

However, if you want to support the publisher/teacher/dharma and get them legally for cheap, check out this website: https://namobuddhapub.org/zc/PDF

You can get books like 'Clarifying the Natural State' (clarifying the natural state was also recommended by Daniel Ingram) and 'Essentials of Mahamudra' for $2 each, both of which are recommended.

I am getting some of the other pdfs.

I confirmed that this website is legit as it is listed in https://www.shambhala.com/khenchen-thrangu-rinpoche-readers-guide/

"Namo Buddha Publications is a 501(c)(3) non-profit,  all-volunteer organization, which was was established to collect and  publish all of Thrangu Rinpoche's books, Audio teachings, Video DVDs,  and practice materials. The royalties and sale of his books go to  towards publishing Rinpoche's teachings and supporting his charitable  activities. The goal of Namo Buddha Publications is to make all of  Thrangu Rinpoche's books, audio CDs, video DVDs, and Dharma photos  available to everyone at a reasonable price."

Nice find. Thank you!

Another mahamudra book recommendation:

https://www.amazon.com/Gelug-Kagyu-Tradition-Mahamudra-ebook/dp/B076GQ6MT4

[8:49 AM, 5/14/2020] John Tan: This book is talking abt anatta and it tries to present as clear as possible the steps towards it without anatta insight.  Means it does not focus on insight breakthrough leading naturally into action but step by step practice into a stage of no mind and explaining the meaning of anatta along the way in the practice of mind.

[8:50 AM, 5/14/2020] John Tan: So the goal of mahamudra is about anatta.

[9:42 AM, 5/14/2020] Soh Wei Yu: Oic.. but lacking insight?

[9:42 AM, 5/14/2020] Soh Wei Yu: Do u think the book is good?

[10:04 AM, 5/14/2020] John Tan: Not that it lacks insight but it does not see how the insight that sees through actually led one towards the meditation they r talking about.  They r explaining the experience and the understanding of view.  But the path prescribed is gradual, it lacks the triggering point.

[10:25 AM, 5/14/2020] John Tan: Go read that book, although dry it attempts to present the way of anatta although the explanation is unclear and not well articulated, for one take has anatta insight, u know what it is trying to arrive at.

Thanks!

Another option might be to check the local online version of your library system. Collections vary between library systems, but worth a look to see if these books are there. There's an app called Libby that lets you login with your library card number and it will connect with every branch in your local library, so you can borrow e-pub versions of books. It's basically the same as connecting to your library's online system, just another way to go about it.