An auto series 1 S14? The looks aren't everyone's tastes, but its legal for P platers in Victoria (under the power/weight limit) and has an SR20DET, while the SR20DET S13 and 180SX's are over the power/weight limit
As KILL HSV said, you could get auto S13's, 300ZX's and Skylines as well for under 18k
Don't forget to factor in insurance, RWC, rego, fuel etc. into the cost
Edit: If you can stretch the budget out a bit, you could get a series 2 S14 (96-98), look better than the series 1