I dont know exact prices but Michaels is defenatly a rip off. A couple of the guys that work there are cool, but they are expensive. Notice I said some, there are like 3 awesome guys and the rest just point to that stupid sign they have.(Something along the lines of youll get good service, but it wont be quick.) My favorite bikeshop in NOLA is Adams Bicycle World in Jefferson. They are very reasonably priced and ALL of the guys that work there want to help you with yo *****. Gerkins Bike Shop on St Claude is a tiny shop like Mike's but hes got a ton of ***** and will bend over backwards to help you get stuff.
And if you are in NOLA come play polo,we always need more people...
And checkout this mini forum, its where some of us NOLA guys are.
http://www.nobikes.org/f/index.php
EDIT: Oh, and I dont know where you pulled $5.50 for a tube at Michaels from. Last time I got one they tried to charge me $9 +tax. It was $2 extra to get a tube with a long valve, it wasnt even a 60mm valve it was only a 42 or whatever it is. **** that! A tube should NOT cost $10.