I'd say that $1100 is at the high end for a good D700 now(now that the D800 is much lower in price than initially and that the D600 is where it is).
Some idiots seem to think that a brand new D700 is going to sell for close to $2400(nowadays!!) when a D800 can be had for a few hundred dollars more
(which is going to hold it's S/H value better in the coming three years!!)
D800 and D600 pricing really puts a brand new D700 in the $2K range maximum, and I'd even say that because the camera is now such old tech(ie. no video, etc) ... it really should be at D600 pricing levels.
1/2 that for a used version ... = $1000 as a real price level. $1100 for a good one, and maybe $1200-1300 max for a hardly used version.
A good point to keep in mind is that a D700 in about three years may only be worth about $500-600, as more and more S/H D800's and D600's appear on the market too.
The question you need to ask yourself Ash is: How much money do you think you can justify in the next 6 months to 1 year for new lens purchases.
I can almost guarantee you that the 17-50 in Dx mode on an Fx camera will be useful to you only in the very short term .. so this if this FOV range was important to you in Dx, it may be one that you might want to update quickly. But you may also want other looks to your images too(eg. wide angle, or wider/longer prime lens shallow DOF rendering too).
If those sorts of things are elements that you may find appealing or interesting to explore, they can be done on the cheap with manual lenses.
Think about where you main usage lies .. eg. if you mainly use the longer end of the 70-200 lens, you may want to look into a good quality teleconverter as a priority.
If you think you may want to explore more widescapes, then obviously a wider lens is going to be a priority.
But the real question is, no matter what you get now, how much do you think you can afford/justify in the next year or so .. during which time you will develop more GAS!!
if this helps you to make a longer term decision and I haven't really checked, but I reckon the Tammy 17-50/2.8(non VC) may sell for about $200-$150 on ebay if you're lucky.