Hey Guys,
You are taking this way too serious IMHO. The French don't dress up to go to dinner as this is a vital part of life and spending time on dressing up is just not worth it. The enjoyment is what comes on the place not whether you wear Bally shoes or Nikes. It also gets VERY hot in Paris (as it is at the moment) so no one wears a tie and suit these days.
Instead, make sure your well groomed and smell nice and that's it.
Now looking at prices. You can go to Grand Vefour and pay EUR 500 pp for a menu incl. wines or head off to Aux Lyonnaise and pay EUR 50 for the same incl. wines and have the exact same experience if not a better one. The French live to eat not eat to live which is a big difference.
It is very difficult to say which restaurant one should go to as there are way too many to recommend and also depending on what you want on that particular day. Often at many restaurants reservations are made on the actual day you want to go out, unless you choose an upscaled Michelin starred place which is popular with visitors...
Now this said, if you want real proper out of this world cuisine, you need to get out in rural France where the best food in the world is made. Lyon (and Aquitaine in the South West) is where it really happens.