Yeah, it's amazing the difference in pricing. For my Fluval 305 canister filter (as an example) Bob's in Brooklyn (sorry Bob, just reporting facts) was charging around $350. Down the street at Petland Discounts, $250. Brand new online from ebay, $100.
LFS' seem like a good place to check things out, but online is the way to go. I used to think it was better to buy livestock at LFS. Then I saw boxes full of fish at my lfs from the same place I was debating getting them from online. Why have them shipped to the store, get acclimated, then take em out and bring them home, and repeat the process? Plus the selection online is superior. Also the employees at lfs are hit and miss. The guy at Petsmart (which I like to get supplies at) at Union Square said the $1/g sale was going on till the end of february (7 weeks later from that day), 5 days later the sale was over, and when I asked why he told me that, he obviously had no idea what I was talking about. So there is a unacountability factor at some lfs'.
I will say that MR vendors seem to have comparable cheap prices for livestock to the online dealers, and of course the customer service/help is usually much better.
My advice, check the LFS for new gear, then buy it online (ebay first).