$100 to spend near 54th & 5th
If it doen't have to be tonight...you can always wait until restaurant week Jan 21-25 and take her somewhere nice and fancy for the prix fixe meal.
but if it had to be tonight try La Mediterranee
947 2nd Ave - Btwn 50th & 51st St...
if you order right, share an appetizer and dessert, you could get a great meal for $100.
Le Bonne Soupe is cute...but can be tight and loud.