Used regulators are the way to go if you want to save money. In general, I would advise a newly certified diver to buy gear in the following order: exposure suit first, BC second, wrist computer third, regulator fourth. The suit and the BC are the most important decisions in terms of dive comfort IMO. You need an appropriate suit for the temps you're diving in and it must fit well. That alone will make a huge difference in dive enjoyment. The BC issue is a little more complicated; I would suggest trying out a rigid backplate/wing/webbing harness rig, as well as a couple of soft BCs, before buying anything. A well designed and properly fitting BC (I like the rigid backplate FAR more than the soft BCs) makes a highly noticeable difference in your buoyancy control and overall feeling of control. This is especially true for newer divers that are still learning to fine tune buoyancy. In contrast, almost any regulator that's in good condition will work quite well for recreational diving. Many new divers have a fear that their reg will not supply enough air or that they'll find it difficult to breathe with an entry level reg. Typically this is not true; while there is a big difference in performance between excellent, perfectly tuned regs and entry level regs (often used as rentals) that are not tuned as well, it's nothing like the difference with a great fitting wetsuit and the right type of BC. The computer is optional of course, you can use tables, but these days so much charter diving is multi-level and the profiles are so computer-friendly that it really does make life easier for recreational divers to use one. It doesn't make much difference what kind you get; they all more-or-less do the same thing and I would not bother with high-end gadgetry. A simple nitrox compatible computer will do the job.
