Cost per seat is not a "typical" metric. Centers usually look at cost per contact, loaded cost per CSR, or even cost per hour. Cost per contact is typically a fully loaded cost, allocating all costs and dividing by the number of contacts. Cost per customer service rep (CSR) may be more focused on salary and benefits, but could include seat costs (or weighted seat costs, if seats are shared).
If you're looking for a cost of the physical seat (nothing to do with the person who sits in it), I would include the technology, real estate, utilities, and potentially any overhead associated with the maintenance of the seat (technology or facilities costs).
This was first published in August 2004