Hi Jiggly
When you say convert, I'm presuming that you're not thinking of doing a foreign licence (ie, FAA) and converting to a JAA licence but choosing one of the handful of schools that offer the JAA licence and just need to get used to UK airspace? I think Ads has said on here that he needed 2 hours (although I suspect Ads is a very quick learner!) Even if you need 5 though, one way to look at is that you take an instructor with you for your first 5 hours post licence at an extra cost of say £30 an hour rather than thinking about the whole cost of an hour dual (you'd be hiring the plane anyway).