Is it incumbent upon me to buy the original copy of the book after I have bought a photocopied version of it due to its unavailability and high price?

It is not permissible to infringe upon the rights of authors by copying books and the like. However, some scholars permit copying books for personal use, not for commercial gain. Therefore, as long as you purchased the copied book for your personal benefit, there is no harm in acting upon this opinion, and nothing is required of you.