And I'm pretty sure it cost a fraction of what FA's hardware costed. Hell, with the disk space and a little extra RAM, I'm sure they could have run on it without having to spend $16,000 of donation money on it.
The physical hardware for e621 was something inordinately stupid cheap, and it definitely performed as such during the last month or so I was performing system administration tasks for Varka in exchange for booze. "Sure, your cheap Taiwanese hardware won't ever fail!"
As a data point, I'm building out a pair of PowerEdge R415's with dual 6-core Opterons, 8GB RAM, and 3x250GB SATA disk in RAID 5 for about $5,500 all in. If I add another 56GB worth of RAM to both of them and throw in a SAN (another, what, $15,000-20,000?), given the performance metrics I've seen for FA, I can host the damnable site three times over, in virtual machines, and still have plenty of capacity to spare.
Protip: Do not develop your infrastructure around your power; instead, develop your power around your infrastructure. If you're constantly concerned about power usage in a datacenter, you're being too much of a tree-hugging hippie. Business-critical systems draw current like a horse drinks water on a hot summer day. That's just a fact of life.