I've very much enjoyed events at Quartino, they do a nice job. So does Maggiano's (on Clark, they have a couple of private rooms). I went to an event at Flatwater recently (on the river at Clark) - the food was much better than I was expecting & they have a large private room with an adjacent bar on the lower level overlooking the river with a nice patio. If you're not foodies its a nice spot for out-of-towners because of the river location (they did a nice iceberg wedge salad with blue cheese, choice of steak or salmon with appropriate sides & then a mini desserts/coffee buffet for us, a group of 80).
Cyrano's (on Wells) also has a private room & should be able to work with your price point. Zed 451 has a gorgeous private space, I've loved events there, not sure about the price though.