Prices are for two people in a standard double room, including tax and service.
Businesspeople descend on Frankfurt year-round, so most hotels in the city are expensive (though many offer significant reductions on weekends) and are frequently booked up well in advance. Many hotels add as much as a 50% surcharge during trade fairs (Messen), of which there are about 30 a year. You can contact the German National Tourist Office for the trade fair schedule.
The majority of the larger hotels are close to the main train station, fairgrounds, and business district (Bankenviertel) and are a 20-minute walk from the Old Town. Lower prices and more atmosphere are found at smaller hotels and pensions in the suburbs; the efficient public transportation network makes them easy to reach.