You're looking at around £800 - £900 for the clutch, flywheel and labour if memory serves me right. That will vary depending on where you take it to get the work done (Nissan stealer or local specialist). Standard advice is as follows - If you need to change the clutch, get the flywheel changed at the same time.
If your buying budget is tight and you're looking at 100k plus Zeds in terms of mileage, which shouldn't be an issue. You do need to be aware of potential expense on things like the clutch / flywheel. That being said, I bought my 2003 JDM on 66,000 miles and she'd just racked up 114,000 still on the same clutch. I am exceptionally smooth though......in terms of clutch and gearbox use that is