Hi Vanessa,
I did a similar trip (Walks and castles of the Moselle) to this region in 2009 and I'm booked on the Ahr Valley trip for June.
On the trip I did in '09 I didn't spend much at all - a few soft drinks and a snack during the day, a beer or two in the evening, a couple of small presents and that was about it. I don't anticipate my spending will be much different this year.
If I do need any extra cash I'll raid the cashpoint but I'm not expecting that I'll have to do that.
Hope you have a good break.
Julian 🙂