I am pretty sure the 'track' rims (18x8) are $1100 each from Nissan. Anniversary are even more still!
But touring rims (17x8) you might be able to pick up for $600 each from Nissan. Though they don't look near as good imo.
For a mint set (no gutter rash, scratches, scuffs or damage) of 18x8 track rims you are looking at $900-$1000 a set. Not bad considering they are $4,400 new from Nissan! But these are extremely rare to find in pristine condition. There are a few around that have damage that can be had for $700-$800, but it's worth the extra dough for the undamaged ones because you will always notice the gutter rash etc on the cheaper set and it will be a constant eye sore.
BTW the track rims look awesome on any Nissan. They are probably the most versatile rim in the whole Nissan range that look good on every car. Seen them on R32, R33, R34, S13, S14, S15, 180SX, 300ZX etc and they all looked awesome. They actually look better on Skylines, Silvias, 180SX's & 300ZX's then they do on the 350Z!