It depends really what you consider expensive.... We really liked Bongo's Cuban Cafe and it's about $25 per person inclusive of tax and tip. You can dine at Wolfgang Puck's for much less and they have a nice variety of choices and 2 locations there.
I like Wolfgang Puck Express in the marketplace (i've never been to the westside). Two can eat very well for about $20 to $25, but this is a counter-service restaurant. RFC would probably be your cheapest sit-down restaurant in DTD.
I like Wolfgang Puck's Express too ... the seating can be kind of limited if it gets busy. We were there for lunch in December and there were only a couple of table left.
Inexpensive, cheap restaurants are hard to come by in Downtown Disney! One night during our vacation in December, we strolled downtown Disney looking for a restaurant to eat dinner. (All the restaurants have a menu hanging up on the outside, so you can stroll by and look at prices.) Just about every restaurant was between $20-50 per adult! Except Rainforest Cafe of course. Planet Hollywood is reasonably priced as well, just didn't eat here because it was a 2 hour wait!!