Probably too late for you but Eurostar are offering cheap tickets to Amsterdam and Cologne from 19/11 to 29/01 at ^89 pounds return.
Must be thalys from Brussels. Buy through Eurostar.
Reference Today's Railways Europe November.
Re if you book only to Cologne you can get a local day rover ticket for local transport around Cologne and Dusseldorf, trams buses, S bahn, RB and
RE▸ . Not
IC▸ or ICE.
Try
http://www.kvb-koeln.de/german/home/ Cologne public transport.
Click on the Union Flag for english version
From the timetable page I got. RE 1 and 5 34 minutes.
Click on ticket helpdesk I got.
Tariff recommendation for Preisstufe 5
1. Recommended ticket combination
Ticket: EinzelTicket Erwachsene
Number of tickets: 1
Price: 9.80 ^
2. Recommended ticket combination
Ticket: 4erTicket Erwachsene
Number of tickets: 1
Price: 35.20 ^ ( Reisepreis ca. 8.80 ^ )
3. Recommended ticket combination
Ticket: TagesTicket 1 Person
Number of tickets: 1
Price: 20.90 ^
Further information
Impressum
All information without liability Einzel = single
Erwaschene = person
Tages = day This will give you unlimted travel around Tarriff Zone 5
Price Level 5 (regional ticket)
^ if the enlarged VRS network (cities and villages of the district
Ahrweiler, involved in the enhanced VRS network, with special arrangements
for job, large customers, students and SemesterTicket)
^ In the education market and in the Rhine-Ruhr cities and municipalities of the
Great border traffic VRS / VRR ", the price level 5 no net force.