I buy a lot from the internet, not just scuba gear. It's a great way to get deals and special, hard to get items. I've recently bought 2 used pairs of ScubaPro jetfins on EBay that were never used (well, you can't tell if they were) and one was $25 and the other $45. There's one dealer in town who sells SP and he doesn't carry the jetfins. Wanted a lot more to order them, too.
I bought my regulator, computer, and BC from a LDS, but I bought my wetsuit at an online place because that same local guy (again the only store in town) had a 100% + markup on the suit from the MSRP and from what every other local shop I asked in the lower 48. I knew my size so that was easy.
What I do is decide what I want and then go the manufacturer to see if they have an MSRP. Then I check the prices at brick and morter stores outside my state for prices. I only have 3 shops available here and they have small inventories and are not distributors for everything that I've been interested in. With those prices in hand I visit my LDS and see what they offer. They don't give discounts or try to match any shop anywhere--ever. So basically at that point I decide if the savings the other places offer PLUS shipping are still cheaper than locally. Almost always is in my case. By over $50. Stuff like dive booties it's more like $5 so that I would buy locally. Same goes for surface marker buoys and masks.
The process only takes about 30 minutes on the internet and I always use the same sites so I don't have to hunt around for online places. I would recommend Scubatoys. They offer a discount to scubaboard members and that offsets a lot of the cost for shipping (depending on what you get). I also occassionally buy stuff from LeisurePro but the savings has to be substantial as their shipping options are a bit more limited and thus cost more. diversdirect.com has a limited inventory in each category, but I just bought my O'Neill Reactor wetsuit from them and the price, shipping, and customer service was great.
Research the prices, check online, check your local shops. Eventually you will see which is the best way for you to go. If you do it well you will save hundreds of dollars. Just don't buy life support equipment from places that don't offer the manufacturer's warranty.
That's my .2 cents