Josh from easywdw.com earlier this year blogged about the affordability of
Nine Dragons and
Marrakesh. I would also add Biergarten in Germany. Its not the cheapest restaurant, but I think its a good value since the food is so filling plus the theming and entertainment are also quite nice.
In terms of QS locations, I'll echo the recommendations for Katsura and Las Halles. I love walking back to Las Halles first thing in the morning and having a relaxing breakfast. Its a little bit of a walk from the main entrance, but its worth it. Also, the sandwiches at the bakery in Norway are fairly reasonably priced, but that could change when it re-opens from its refurb.