Thoughts on ND Filter?

[F8&Bthere]

I want a 77mm threaded ND filter for a wide angle lens. This would be for landscape shooting outdoors, to blur water etc. I don't want a set really because I hate fiddling with small things like that in the field. So I thought the perfect thing for me was this Singh-Ray Vari ND filter I've been hearing about. $500? Are you kidding me? I can buy a freakin Gitzo tripod for that, or 3 x Nikon/Canon 50/1.8 lenses!
So I'm thinking that I might just buy one decent ND8 and because my camera has very good high ISO performance if the 3 stops is ever too dark and can just vary my exposure in camera to lighten up. Anyone see flaws in that logic, aside from me being a cheap SOB?