The "suggestion" of using 35 watts per drive is WAY too much. 24 watts is a fairly common number and it can get as low as 5 watts for some 2.5" drives. I spent the time creating a spreadsheet that provides that vendor supplied startup power usage and for the 5400/5900 RPM drives it can go even lower.
The average startup power is 21.81 watts for 62 drives. This is 13.19 watts less then the suggested 35 watts!
Take a look at the Disk Price Analysis spreadsheet in the resource area to get actual numbers.