Question: IS THE PRICE PER PAIR OR EACH
Answer: Thank you for your inquiry,
Yes sir, an APC AR7221 kit (currently on sale for $160.00) includes: Qty 2 - 42U Vertical Cable Managers, Installation guide, Mounting Hardware, Qty 6 - Cable retainers with snap hinges, and a Top securing bracket.
Question: At 35" high I would need to order 4 per cabinet ? 2 on each side?
Answer: Thank you for your inquiry. If you desire cable management on both sides of the rack, yes, two sets of two 35inch Vertical Cable Managers would be required. Typically however, we see installations on only one side.
For your reference, here is a link to the installation guide:
http://www.apc.com/salestools/MLAN-967N8J/MLAN-967N8J_R1_EN.pdf