A 15 k z will be a decent starting point but quite honestly when compared to newer cars you will notice the issues and start pouring money into it. Case in point. I have 4 z's at this moment. 1 is a 95 tt which is bone stock other than wheels and the head unit, jdm nose and tails. Over time I have over 20 k in this car. Ridiculous I know but I have been working on making this 20 year old car look and feel like new. I even has very low miles but age takes its toll.
In short figure out how much money you can burn literally and drop that on a 20 yr old car.