I often get asked about how much to budget for a trip. The answer is very personal. Some people drink a lot, others barely drink. Some like to shop, some like cheap cheesy souvenirs, others like to make a big purchase. Then there is eating, some like to grab food at the grocery store and picnic, others want to have a nice sit down meal. Depending on the answers to these questions, your budget will be either higher or lower then my standard answer of $100 a day. One thing about tours though is that you'll often have full days in cities, and then spend the days inbetween as bus days. Bus days tend to be cheap, usually you're just paying for a meal or two, snacks and maybe a random souvenirs. Days in cities can be much more expensive - food is more expensive, attractions, more souvenir options (and more expensive ones).
Often when I get home I will go through my receipts and get a sampling of costs. For this trip I was really good with some stuff, and not so good with other stuff. But here goes: (all prices are in pounds)
Holyrood House 10.25
City Cruise (London Eye to Tower) 5.36
Day Pass for Tube (off-peak) 5.60
Edinburgh Dungeon 15.50
Camera Obscura 9.25
St. Pauls 11.50
Edinburgh Castle 11.90
Hadrian's Wall 4.80
Celtic Necklace 10.00
Rugby Shirt 15.00-30.00
Dinner with a drink at Giraffe 13.70
Scarves 10.00 to start
Postcards 35-50 pence
T-Shirts 10.00 to start
Stuffed Animals 5.00-15.00
Glenlevitt Whiskey 28.00 to start
Tea 1.00-4.00
Soda 2.00-4.00
I didn't actually price beer and alcohol. I do remember some places being pretty cheap - 2 pounds or so for a drink, while other places might be 4 or 5 pounds.
Food was pretty expensive. Meals for lunch at a cafe usually ran 5-10 pounds. Dinners often started at 10 pounds. Tea with a scone usually cost around 7 pounds.
I spent a little under 900 pounds for the whole trip, which included my hotel in Edinburgh for 2 nights after the trip. 2 full days in Edinburgh and London before and after the tour (no meals provided). Taking out the hotel, my costs were about $100 a day. While I'm not a big shopper, and not a big drinker, I did do some shopping and I do drink more on tour then I do at home. I also like to have good meals. Also, I did find attractions in London and Edinburgh were expensive.