25K will get you a good fast Zed that's for sure. You would want to find something someone might have spent around 40K on, done a bit of sprinting in it and sorted out all the gremlins. If I was you I would visit a couple of track days at Phillip Island & Sandown and have a chat with some of the Zed owner/sprinters. Everything is for sale for a price or they might know of someone. Definately don't rush into it. For that money you definately want the car good to go with virtually nothing more to spend. The engine and it's mods/HP would obviously be another key point.
My brother (Gordons) Blue Zed was not built as a racer. It's more a nice clean/straight, no rust, good disks all round, coil overs etc but not a hot motor. He was talking around 27K to me last weekend. But I told him he was crazy selling it after working on it for 2 years and not even driving it. Too busy with other cars. Ha.
Anyway have a look around and even enquire interstate. I know there are some awesome machines there as well. (Zed Websites). When you find one and close to making a purchase then give us a yell on here and some of us might either know the car or at least advise if it's a good deal. I am definately not the expert in this field but between many of the active members you will get a good heads up.
Hope that helps. Regards