It's normal to save up to 40% off gear by buying it online but there is a hidden and indirect cost to doing so. This is one of the most controversial subjects in diving today.
The existence of our local dive shops depends on us purchasing gear from them. If the majority of divers were to begin buying most of their equipment on-line, our local shops would go out of business and would no longer be a source of air, charters, service and advice. I know it's hard to notice the impact of the decision on one diver and the cash saving are very tempting but each of us have a much stronger impact than we may realize. It the same reason we don't litter, vote and try to be polite while driving.
Last week I spent $680 for a Scubapro MK20/S600 regulator from my local shop. I could have bought it online for $450. I didn't do it in the interest of the store owner or his staff but for myself and for other divers in my area. The benefits of buying the gear from the store outweigh the extra cost. Plus, I don't ever recommend buying gear online and then taking it into a shop to have it serviced.
If the extra cost is a very strong issue for you my suggestion is that you purchase gear on-line that does not need to be serviced and that you buy your tank, bc, regs, and computer/gagues from the shop that can offer the best prices, seem to be polite and knowledgeable, and that isn't so far away that you won't use them in the future to get air, etc. But don't expect a discount from a shop if you're a first time buyer and aren't buying your gear as a package.
One additional suggestion....if you are ever thinking of even possibly getting into tech diving, this should influence what gear you get now for recreational diving, especially for your bc and regs. It'll save you money now and in the long run. Though your local store may try and talk you out of it because many are unfamiliar with the steel back plates and wings tech divers use, it just as safe for you to dive with them on dive #6 as it is on dive #600.