Except for the part where most local headshops simply buy their pieces from sites like these and then mark them up a bunch. Might as well cut out the middleman.
what you have to look at carefully is shipping and handling. Stupid to pay more for shipping then the item you want. Never understood it. I know that some places use that as a method to off set the cheap price of the item you purchased. With that said, dhgate to the dot to the com. It is a portal to all things Chinese and Asian in general. One can find some pretty amazing and incredible things there if one knows what they are looking for. That's another conversation for another time heh heh heh. Just search for glass water pipe or similar at the main page search bar. Categories drop down from there. Sometimes a vendor only sells quantity so be sure what you're buying. You can often times find free or super cheap shipping so don't buy the first piece you find because there are tens of thousands of items to look through. Good luck blade.
My LHS is marked up a little, but within reason. It is nice to be able to actually hold the piece and examine it closely. My only gripe is that they didn't have exactly what I was looking for. I think more realistically if you want a quality piece, you need to consider the $150-$200 range both online and at your LHS. I think sub $100 is a gamble, and at the very least severely limits your selection.
Grasscity is fine if you don't mind waiting a month for your package to be cleared by customs. I recommend ThickAssGlass.com, I have never heard of any complaints about them, and they ship from the U.S. They sell their own proprietary pieces as well as pieces from other manufacturers. I would use a reputable site, just so I know that I will have good customer support in case anything goes wrong. i.e. broken or missing items.
I've had many purchases from jupitergrass.ca as well as smoketower.ca Just look at the specs and look in the sales tab and you'll find something fun