Go to the publisher's site. The 2020 or 2022 edition costs around ₹500 ($6). But a ? That is ₹50 on Amazon or Flipkart. Scan the chapters you need for the semester at the college photocopy shop (usually legally allowed for 10% of the book).
As for downloading the PDF of RK Gaur and SL Gupta's book on engineering physics, I would like to clarify that I couldn't find any direct links to download the book illegally. However, I can suggest some ways to access the book: Rk Gaur And S.l. Gupta Engineering Physics Pdf Download