"reasonable" group dinner
Dante's Kitchen is Uptown near Tulane and serves a local farm vegetable plate entree as well as local farm vegetable sides. They have outdoor dining and should accomodate your group. I don't know how much watching your wallets means. You may have to go to Felipes if Dante's is too expensive. Lebanon Cafe is inexpensive Middle Eastern food and serves a vegetarian entree. It's in an attractive location Uptown on S Carrollton. And Jacques INO's would be a good choice. They take reservations only for a party of 5 or more 30 days in advance for dinner only. You might have to ask about a vegetarian entree though.
Dante's Kitchen @ 736 Dante St., New Orleans, LA. 504 - 861 - 3121.
Felipe's Taqueria Uptown @ 6215 S Miro St., New Orleans, LA 504 - 309 - 2776.
Lebanon's Cafe @ 1500 South Carrollton Ave., New Orleans, LA 504 - 862 - 6200.
Jacques - IMO @ 8324 Oak St., New Orleans, LA. 504 - 861 - 0886.
Not sure exactly what you consider "reasonable".
I would assume if you're tulane alum you might like to gather uptown and get some nola food if you're in from out of town. Vegan is tough in new orleans though.
Joey K's on magazine has a pretty extensive new orleans based menu at a good price point in my opinion.
Ye Old College Inn has gotten a little bit pricey but the po-boys are huge and a better value, the upstairs area is nice for a group dinner.
These both meet the casual/price criteria, but are probably not the most delicious (not bad, just not great) or vegan-friendly, however I think both would be willing to cater to the vegan.
I would suggest Boucherie, but it's pretty meat-centric and tough for bigger groups...
Joey K's Restaurant & Bar
3001 Magazine St, New Orleans, LA 70115
8115 Jeannette St, New Orleans, LA 70118
Domenica is reasonable, and while it doesn't have too many vegan-friendly dishes on the menu (but several vegetarian options), the food, including salads, are delicious. If you called ahead, though, I'm pretty confident that the chef could come up with something very tasty for your vegan.
123 Baronne Street, New Orleans, LA 70112