I love Germany, probably my favourite country on the continent (apart from football reasons of course). Great beer and very friendly people, particularly in the south. Its probably too much of a detour but Munich is one of the best cities in the world imo. Fantastic beer halls and some great countryside surrounding the city.
If you're going via Calais you could take in Koln, Dusseldorf and Berlin on the way (maybe even Hamburg) which would be a good road trip.
If you go to Berlin you should take a segway tour of the city. It looks ridiculous and isn't cheap (around €70) - I had to be dragged kicking and screaming by a mate but it was awesome and I'd thoroughly recommend it: http://citysegwaytours.com/berlin
In terms of cost, its similar to here. Maybe even slightly more expensive with the :censored: £ to € exchange rate. In the city centres its €3-4 for 500ml of beer but if you don't mind going off the beaten track a bit you can find some great little drinking holes - when I was in Berlin around 12 months ago we found a dingy place selling great beer for €1.80. Stayed there all night and got wrecked!
I'll echo the comments made by leeslover - the food isn't great. Obviously they have some decent restaurants but the pub grub tends to be a combination of boiled sausage, sauerkraut, schnitzel and fries. It makes good drinking food and certainly isn't inedible but you get sick of it pretty quickly.
Where abouts in Poland are you visiting?