I got my '95 R33 GTSt 5sp late last year for $17,000 (stock as a rock) off a private importer (avoid dealerships) he was nice enough to throw in 12 months rego and pay all the stamp duty etc. (saved me $1,000–$1,500)
It had 60 000 kms on the clock but I would disregard the K's on imports... just judge by condition of car...
If the car is stock make sure there is no previous signs of modification ie there used to be a FMIC but its not there now. (This usually means the car was boosted...)
It might also be worth paying a little bit extra to get a '95 model as they came with a few extra goodies (Like series 2 rear wing, airbag etc)
My best advice would be look at a lot of cars and don't make your mind up before you go just get the best condition car for the best price... not just visually make sure it still hauls ass...
My mate got a '93 for $14,500 with zorst, two stage boost control, 17" rims, lowered springs/shocks, POD...etc... mainly because he busted the guys balls and he really wanted to sell... so I think $19,500 is plenty...however allow at least $3,000 in on road costs...unless you can get the seller to throw in rego etc.
Oh and 180's kick ass but generally get less respectful treatment by there owners than Skylines...
Hope that is helpful