I generally take out-of-town clients to the North End, which is close to downtown. There are some moderately-priced Italian restaurants like Bacco and Marco, which have decent food and a nice atmosphere. I also like Petit Robert Bistro and Eastern Standard in Kenmore, and over in Cambridge, I take clients to Central Kitchen and Rendezvous. The entrees at Rendezvous are in the mid-20s, so it may be a little beyond the budget.
Not downtown but over in Charlestown is Navy Yard Bistro. They have great food and reasonable wine list. They are located in a historic building.
For decent food, low prices, and a room that is far nicer than it deserves to be, Laurel on the Back Bay/South End border is nice.
I really like the Eastern Standard recommendation.
If it is a small group, a place like Pops in the South End may work.
Near South Station is Les Zygomates, which is a bit more expensive than these other places, but has a great and affordable wine list.