If you want to have the meal and view of a lifetime, eat lunch at Jules Verne
in the Eiffel Tower. We prefer it to dinner for the economy, but really for the view during the day and actually seeing the city. I think for lunch it would be about 200E with a glass of wine.
Le Train Bleu in the Gare de Lyon would be fun for the Belle Epoque décor--we had a drink in the lounge and loved watching the Parisians arrive for lunch and imagine it in the grand days of the last centrury. Our favorite place is La Florimond, near metro Ecole Militaire. We celebrated DH's birthday there. It is small, intimate, great food (about 35E prixe fixe) and affordable.
A great place we found was Au Piano Muet on rue Mouffetard--a raclette restaurant. VERY inexpensive.
you are going at a great time for the dollar.
The Bistro du Septieme is fun. A classic bistro open on Sunday (make reservations) is Fontaine de Mars. All a la carte--had delicious foie gras and cassoulet there.
Eating lunch at great places can be a way to have the experience more affordably.
And we make a trek over to the Gare du Nord every trip to eat mussels on the terrace facing the Gare at one of the several cafes there--Maison Blanche is one. Of course, you can get mussels just about anywhere, but this is our way.