The Fairmont Copley Plaza
Want to get dinner gift certificate for close friends spending a restful wkend in Boston. (Xmas present from the in laws). Looking for a place w/in walking distance of the Fairmont. She's vegetarian, he is not. Looking to spend ~ $75. Not big drinkers.
That kind of money will go far at Coda, which is an easy walk, a casual but nice-looking bar/restaurant that always has some decent vegetarian options. I'm also fond of their thoughtful, budget-priced wine list and pretty good cocktails. Menu here: http://codaboston.com/dinner
It tends to get mixed reviews here, but Laurel would meet all of your requirements and I have always had a pleasant experience there.
A little farther away but still walkable and reaching the top of your budget if they don't drink and order wisely would be Hamersley's.
142 Berkeley St., Boston, MA 02116
553 Tremont Street, Boston, MA 02116
Brasserie Jo is a fairly close and qutie pleasant.
If the vegetarian is a pescatarian (eats fish but not meat), then you might want to consider Legal Seafoods (there is one nearby in the Prudential Center).