I think in your pre-tour paperwork Rick recommends about $50/day for extras and meals that aren’t covered. I’m not home to check my notes (yea!!!) but I think I came in around $25/day in 2014, maybe a little less.
I DO recommend doing anything extra the guide offers. Mine offered to take folks up the Schilthorn early on the free day then take us up the other side of the valley for the Mannlichen-Kleine Scheidegg hike. The cost for the gondola to the Schilthorn then the cog train up and down plus a gondola segment was a tad expensive but SO worth it. The expense that day was way over $50/50 Swiss francs but it evened out over the whole trip. Ditto the gondola ride in Venice, expensive but fun.
BTW, the guide will discuss with the group on the way to Switzerland how much Swiss money you should withdraw based on different scenarios.
So, I’d have a general daily budget knowing it will fluctuate day to day. Some days if you’ve had a big lunch you may go for gelato for dinner, lol!! That’ll even out a more expensive dinner or fun activity.
If you can add a night or 2 beforehand do that. It’s really good to give yourselves some flex time for travel hiccups and to get over jet lag before the tour starts.
If you have the time and budget, also add nights in Paris!!
One of my very favorite tours!
Editing to add: i just went back to read my trip report from this tour. While I didn’t seem to mention how much money I averaged per day, I decided the advice on the thread (others added in some thoughts as well) was still relevant. And yes, makes me want to do it again!!