if you want a 4v... like chicken said, get the cobra. Shoot for an 01 cobra; it has an IRS, 31 spline diff and better seats... plus, a bit better head and intake design than the earlier 96-98. In the long run, it would be cheaper, and you're in reality getting a better platform. (cobra's have, since 96 had a 4.6L 4V, but the car itself really came into it's own for suspension (IRS) and durability(31 spline over 28 spline) in 1999 and 2001 respectively)
Another option would be the 03-04 Mach 1... this runs what is essentially the same cobra engine block from the 99 and 01 with the even better heads from the 03-04 but it has a shaker hood scoop (functional) with a solid axle rear end. And last option... 03-04 cobra; these have the super charger and 390HP with IRS from the factory.... they are also listed in ascending price range.
Of course, if you really have the money... and can find one of the 300 year 2000 Cobra R's... you'll get a 5.4L DOHC and all the goodies that came standard later in the cobra life span such as IRS, 31 spline and Brembo brakes. But don't go looking for a back seat, air conditioning or a stereo to be included!!