All the stores pay near the same price for LeeMar tanks. Some stores feel the need to make the most possible on tanks while others believe that they'll make it up on the rest of the equipment needed. The flaw in that logic is if the buyer is looking for the absolute best deal on the tank they'll probably follow suit on everything else.
Then it just comes down to are you willing to pay more to buy it from someone that you can/will deal with long term.
With tanks I think you need to keep in mind that in most cases any problems that might arise will need to be solved through the point of purchase and not via direct contact with the manufacturer. That's where the relationship between you and your retailer becomes vital. Lee Mar has had their share of problem tanks in the past and from what I've heard they'll almost always fix that problem as long as you tear it down and send it back (you pay the freight).
It's my opinion that sometimes Lee Mar pushes the envelope as far as tank engineering goes. I've seen other name-brand manufacturers refuse to build a tank to the customers specs while Lee Mar had no problem making it. We as hobbyist need to trust the judgment of the manufacturer when it comes to glass thickness, brace widths, etc.
SteveU