Just thought I would add some comments to this thread. I have been to NOLA a couple of times in the last six months since my kid attends Tulane. Almost all of the restaurants mentioned here are fine choices for a good meal. I noticed that August
http://www.rest-august.com/ was mentioned by a few posters and it is a fine restaurant, but I think you would be hard pressed to get out of there for $100 for two people, unless you just get an entree, a glass of wine, and maybe dessert. His entrees are in excess of $30 and his five course tasting menu without wine is $70 per person. His Degustation menu is $150 per person. Depending on how you dine (and drink!) you might be able to top $100 for two at more than a few of the places mentioned.
As for jackets, of the places I've been to, Commanders Palace
http://www.commanderspalace.com/new_orleans/index.php and August would be the two where I would consider a jacket. I will say you could probably get away without one if you are dressed nice. Commanders web site says jackets preferred at dinner, but I saw people without them seated on a Saturday last time I was there. I think post-katrina things have gotten less formal. There are few restaurants that will turn away a nicely dressed non-jacketed customer with money in their pocket now days.
A place not yet mentioned that I would recommend is Stella!
http://www.restaurantstella.com/ in the Quarter. We had two great meals there. Gautreau's
http://www.gautreausrestaurant.com/ has been mentioned and we thought it was great also. Cuvee
http://www.restaurantcuvee.com/cuvee/ was another place we enjoyed. The one place mentioned above that did not really impress me for dinner was Herbsaint. We waited forever to be seated (with a reservation), the service was mediocre, and the food was nothing to write home about. Since I was only there once and as I recall one of our appetizers was really good I won't totally pan them, but I could not recommend them either.
New Orleans is a great place for food and you should be able to do some great dining there. As you can see almost all of the good restaurants there have web sites, check them out, especially the menu prices if you are trying to watch the dollars.
One final thought, New Orleans just got the dubious title of number one crime city. While it is not as bad as all that, I would recommend that you be aware of your surroundings and try not to stray too far from the beaten path. You can easily go from a good area to a bad one in the matter of a few blocks. It is the same advice you would give anyone in any big city. But if someone tries to tell you where you got your shoes, just keep walking.
Ian