I'd say that even if you can find a slightly better price on some of these online shops, consider the support you get at your local store. If they're willing to talk to you and guide you through questions, using up their time to make sure you can be successful in the hobby, it's worth those extra dollars to support them.

I have a local freshwater place for my little freshwater tank that I go to frequently because the guy who runs it is amazing and spends so much time supporting me with my questions. Unfortunately the saltwater shops are a lot farther from me, but if I'm not in a rush, I'll stick to them over a website where I may or may not receive support (not saying there aren't any good online shops, there ARE good ones).

That being said, comparing prices online is still a good practice at the same time. My story would be different if the price difference was like double or something nuts lol.