These cars are tinker toys... there is always something that needs to be worked on. The good part (for the early Z's) is that they are simple to work on once you get your hands dirty. Just a handful of metric tools and a shop manual will get you a long way. It is a great car to learn the ropes on. I would advise you to buy something that has spent it's life in the southwestern part of the country though... Arizona, New Mexico, etc. You'll be SOOOO far ahead in the long run. My 240z I bought here in Florida for $800. I drove it for 6 months until I drove through a puddle at around 40mph, and water flew up from under the passenger's side floormat and hit me in the face!! I started on what I thought would be some minor rust repair and ended up replacing the floors, framerails, rockers, rear quarters, inner wheel arches, fenders, doorskins, and hood. For what I spent on that I could have had a really good starter car from the southwest. Hindsight is 20/20...
As far as what I have in it now, well, I have a ballpark, but try not to think about it too much. I throw all of my receipts in the circular file... I will never get out of the car the money that I have in it (not to mention the time), and having the evidence lieing around is just bad news (My wife a couple of weeks ago came across the receipt for my new CCW's - OOPS!!)
Good luck w/ the hunt for your first Z car and be patient...