Ooooooohhhh I really want to do this gig anyone travelling from Lancashire give me ideas of prices to make this doable??? 
In recent years it's been either Flybe Manchester to Dusseldorf and then get the train direct from the airport train station to Cologne or German Wings Manchester to Cologne. Never usually much on a Saturday if I remember rightly (I think they are mainly aimed at workers/commuters), so you might need to factor in 2 nights accommodation. Flights, reasonably priced if booked in advance and you don't bother with checked in luggage or bothering about picking a specific seat, food and the like.
Cologne is popular at this time due to the Christmas markets, so accommodation isn't the cheapest. Various options around the train station (including the side furthest from the city centre) or a bit further out. Usual chain type places + plenty of independents. Or there's a few hostels that also have private rooms, some en-suite. The public transport is fine, as you'd expect, so no need to worry if you get a cheaper hotel option that's a bit further out. Quite a few use IBIS Messe Duetz just over the river from the train station, but I haven't used that.
We usually don't bother with Paris and just go to Cologne for an extra night. However this time, with Paris being a double nighter, we're doing that and so will be on the train from there to Cologne.
H