Living near Thessaloniki I have never had the chance to try the hotels of town. As far as I know, the big and/or luxurious hotels are rather colourless, especially Macedonia Palace and Capsis. For descent single rooms estimate from 40 up to 160 euros.
For a rather upadated hotel list check the link below....
Theme: Hotel
Comparison: about average
Directions: Hotel 'Electra Palace' has the best location right in the middle of the city, while 'Mediterranean Palace'(tel.+30 2310 552 554), just in front of the city harbour's passenger terminal, is the newest.