I try to support my LDS as much as I can, because: 1) The owner is a really nice, helpful guy, and I KNOW he doesn't make that much money
2) If the LDS goes under, where will I get my tank filled, where will I get my gear serviced? (If you live in a town with multiple LDSs this might not be as much of a concern, though.)
However, that said, I can't always afford to pay LDS prices. This is the compromise that I more or less work with:
If it is a purchase of anything that a malfunction would significantly affect safety, especially if it involves AIR (regs, bc's, tanks, computers, drysuits) I buy it from my LDS. THen I KNOW I can take it there for inspections & service, and I know it will be well-taken care of, and any problems means I can take it back to them. If it is something that is less safety critical, or has less possibility of malfunction (e.g. fins, mask, snorkel, wetsuit, weights, lights, knives, luggage etc.) I buy online.
What this means is that all the MOST expensive stuff comes from the LDS, but with it comes a good measure of peace of mind. The online purchases of other gear helps offset some of the increased LDS cost. Also, I occasionally will buy something on-line if my LDS simply doesn't carry it (or anything similar to it) but the little things like lanyards, clips, wetsuit shampoo, etc. I still buy from the LDS, because even if it is more expensive, they're still cheap enough that I can afford them, and like I said, I REALLY want to support my LDS.
Safety is the most important criterion for me. And I think that LDS purchases are really the way to go with anything my life may depend on.
otter-cat