The 4* hotel is located just outside the city centre and gets good reviews. Double room for 2 nights works out at £97 for 28th to 30th March. Just over 20 minutes by car from the airport.
Return flights from Stansted to Cologne £10 each - sample date 28th March to 30th March
There are various £10 return flights in March from Stansted to Cologne including most weekend dates. Based on hand luggage.