Cheapest online store to buy a D800?

It seems that this may not fit what you're asking for, but on a body like a D800 the tax is a fair old chunk so I'd look for a reputable dealer that gets around that to be honest.

The refurbished stuff is a whole different matter with varying pros and cons.

If I had the money tomorrow I'd order from Beach Camera in New Jersey. A good reliable company with an actual location if anything goes really wrong.