Good B&B in Nurnberg?

On the whole accommodation in Nurnberg is very affordable. There are three different Ibis Hotels located near the main train station (which is across the street from the old-city) typically rates are around are about 99 euros. Off-season you may be able to get rates like this at the more plush business class hotels in the same area like the new NH Hotel.

Check IBIS

If you're into the hostel scene (I'm not), part of the Kaiserburg serves as a youth hostel. You can't get more of a central location than a castle standing upon a hill in the middle of the city.

Mary, Nuernberg has a website in English, they redirect you to the tourist office for accommodations - this site also has an English version. Plug in your top price for a single room - I used 65 Euro. This resulted in 102 listings (the last few in sourounding areas.) These listings give you a price range and also give you the price for doubles and tell you the distance from the train, the convention center and the airport (in kilometers.) I assume "train" means the main railway station. I had to hunt for the tiny arrows that let you go to the following pages but they're at both top and bottom of page 1. I bet there are cheaper rooms, too, if you play around with the site.