Where should I buy?
Why the lds's are so expensive?
Not all LDS's are expensive, but the issue is sheer economics. Most LDS's do not do the amount of Volume the larger online stores do. The larger volume brings the ability for the larger online stores to lower their margins which in turn makes it "Cheaper" for you. Most LDS's do not yield the same volume so in some/most cases they have to have a larger margin on average comparatively speaking.
Also, in my line of work volume brings larger discounts from the manufacturers along with SPIFS/Rebates so the larger volume dealers may have an advantage. ** NOTE: I am speculating as I own a network engineering company and not an LDS.
Why some people are afraid to buy online?

This is a conversation past Scubaboard.com

If I can buy a Car online in California and have it shipped cross country all over the Internet, then I am good with buying Scuba gear online.
What is the truth? Which is better?
Value is in the eye of the beholder. Personally I buy 98% of my gear from my LDS for two reasons.
#1 they come within 2-5% of the best online price and they do "the little" things for me at no charge. Ie. If something is on backorder they lend me theirs to use.. Ie. I get free Nitrox/Air fills
#2 they "Consult" with me based on their experience. My LDS staff are very experienced Instructor Trainer/Rebreather Instructers, Trimix, etc. After spending time with them after I research on the Net (Scubaboard etc.) I am pretty much making the right choice everytime with them. This prevents me from buying Twice which is MUCH more expensive than the 2-5%
I do buy "pots and pans" items from various online stores such as Leisure Pro, Scubatoys, and Scuba.com. I buy things like hoses, SS Bolt Snaps, and other like items. Usually this is me at 1:00am surfing the net trying to get "accessories" when my LDS is closed.
Tell us what you think and tell your experience about it.
Bottom line is do what you are comfortable with and if you pay for value then ensure you are getting it no matter where you are buying!