LiPS are selling the dye throttle 68/4500 for like, 140 quid.
Though it'd probably be alot cheaper to look for something thats olnly got a few years 'till test in the classifieds.
For a 4500psi 68 bottle with a couple of years left on it you will looking at around £70-£80 depending on make and condition.
Just keep an eye on the forsale section on the forum mate.