As a owner of a Dive Center in Ann Arbor, Michigan which has an online shop... I can tell you that if you saw my compressor, electricity, filter and oil bill you would know without a doubt that we cannot survive on air fills...
After we pay the insurance and pool fees we cant make all that much on Lessons either....
So piping in, give your Local Dive Center a chance... tell them what you are looking for, ask their opinions and, most importantly, if you are going to buy it somewhere else, online or otherwise, give them a chance to do good by you... if they don't or can't ,they cannot hold it against you.
With the economic climate the way it is I am sure that we are going to lose a lot of LDS in the next two years... we have lost 4 in the past year in my area... there are people who drive over an hour to get air fills at our quarry because their local dive center is gone. Look at where you get your airfills and think of what you would do if that shop was no longer there... and give them a chance to do what you want them to do.
My 2 cents... Thank you for your support.
Rich