Fantasea makes a housing for the D70 this is under $1000, and includes a port for the kit lens. So for $2000 you can in fact come CLOSE to getting the D70, a reasonable usable lens (18-70mm I believe) and a housing with a port.
Now here is the kicker... You need something to haul all this stuff in. I'd plan on $200, maybe more. You need at LEAST a 1 gig card... another $90, maybe less. You really want a strobe... There are some available for under $300, but $250 is about minimum. You will want a second battery. I'd look at aftermarket batteries as they are a fraction of the cost of the Nikon branded batteries, and most manufactures don't actually manufacture their batteries in any event. More, how about a good UV filter for the lens as protection, a sensor cleaning kit of some type, upgraded memory for the computer, a lens pen, or lens cleaning kit, photo quality printer, ink (expensive as all ELL), paper, the list can become daunting. Not trying to bum you out or anything, but don't kid yourself, getting into photography with a digital SLR especially UW is NOT inexpensive even if the bodies run under a grand. And even if you get EVERYTHING on my list above, you still only have one low end lens.
Unfortunately this is why so many of us who already own DSLR's and love photography opt for PnS solutions UW. I would have loved to put my D1x in a housing, but for 5K, hmmm. When we move to FL (which we have plans to do in the future) then I'll be diving enough to justify shoving a DLSR in a housing. For now, my S70 is providing memories, and getting me comfortable with UW shooting.