The price for the latest year  is $40 and all other back issues are $20 each. 
Order Directly from RIT Press.

All issues of the New Series (except nos. 2, 6,7, 8, 11, 13) are still in print and available for purchase.

All issues of the Original Series (except nos. 5, 6, 7/8, 10-14, 18, 23, 25, 30, 38/39, and 48) are still in print.

Note: the following are double issues: nos. 26/27, 31/32, 43/44)

Back issues of Printing History are indexed in Library Literature and the MLA International Bibliography.