I found the hotel food to be quite affordable -- but it is four star quality and I'm from a country where eating out is expensive so your mileage may vary. The portions are great and you can always ask for a doggybag to take some to your room. I had a way too big pizza and they packed it in an insulated box so my pizza stayed nice and hot *wag* Excepting the French restaurant, the hotel restaurants were cheaper than I expected, anyway.
We went to the Chinese restaurant already mentioned here. TBH we feared for our stomachs for a bit when she threw a cleaning cloth at one of the people in our company to clean the table...it was also deadly quiet with no one there...you could hear a pin drop...that is until she put on the Chinese ABBA muzak...(Seriously weirdest food experience I had xD)
However!
EXCELLENT FOOD! We came back a few days later and the kind owner? recognised us. She doesn't speak German or English too well but she was smiling and going all "ohh you came back", it was nice. The food was affordable and honestly good. First actual spicy food I've had in Germany. Way more than I could finish, too
The restaurant itself is just oddly quiet and you might end up listening to ABBA muzak but hey. Neighbourhood is a biiiit shady but I just put away my badges and went with a group, no problem.
edited to add: am a bit fuzzy on price details but if I am not mistaken, around 7 EUR got you a huge plate with rice, veggies and meat