Dinner near Fairmont Château Laurier, Ottawa, ON
Phelana, try out Sweetgrass Aboriginal bistro 108 murray street. They're open for lunch mon-fri, open for dinner mon-sat.
The prices for lunch should be able to meet your budget, and its definately not your ordinary restaurant.
Here's the website www.sweetgrassbistro.ca
Not too far down Elgin street (directly south of the Laurier) is "The Manx". It is pub-style restaurant that does excellent brunch and dinner, fusion style. It is a very small space and tends to be packed with a semi-trendy crowd mix of drinkers and diners. I recommend the lamb curry wrap and the specials are always great for dinner. Their brunch I'd recommend more highly, the eggs benny are great and affordable. I can't see you spending more than 40 pp including a desert. As i said, it is more trendy and casual but in my mind better than most of the "higher scale" restaurants in Ottawa.
n.b. brunch is only served on weekends, although i think they have a good lunch menu as well!
and lunch at the café in the large glass-domed space in the National Gallery is also very nice. Small but tasty menu, excellent service, and a view over the river that can't be beat.
For lunch or dinner on a warm summer evening, any of the restaurants that share the patio behind Social, which is on Sussex quite close to their hotel, would be very nice. There are 4 restaurants there, it's a pretty courtyard, and one can just check the menus and make a choice of which resto to eat at.