To have an SPS dominated tank that size is gonna take a lot of soldering.

Probably on the order of 300 LEDs. It's hard to talk specifics without getting a lot more in depth.
FWIW, my 360g tank will be a mixed reef, and I'm planning on 180 - 200 LEDs. It's 6' x 4' x 2'. If it wasn't for LEDs, I would probably do four 250w MH with a few actinic VHOs or T5s. Total power consumption for that rig might be ~1200w. The LED rig I'm planning will be more like 400 - 500w.
If you're paying the national average in power cost (around 12 cents per kwh), and lighting the tank for 10 hours per day, that's a difference of 84 cents per day. Doesn't sound like much, but over 10 years, it's ~$3k. If you consider lamp cost, the 4x MH lamps I would have used probably cost ~$75 each, and require replacement once a year. The fluorescents are probably another $100/year. That's $400/year. So, my total savings over 10 years would be roughly $7k. Your case would probably be similar.
Of course that's not factoring in component failure and other things like that, but it's probably fair to assume that both systems would eat parts at comparable rates. Regardless, from a financial perspective, the LEDs are clearly going to win.