Hi Jim,
I'm looking forward to Alan's response as well, but I can readily say I make do on as little as USD$5-$10/day when touring, which is pretty close to Alan's £5 after exchange rates (£1=USD$8.01 at the moment).
I stealth camp the vast majority of the time, so have no lodging costs. I may do a motel once a week less, but they are usually the budget ones in small towns, and they run as little as $35-$45/night and include the bed (of varying quality...to the point where I sometimes still sleep on my pad on the floor, and in my silk bag liner to avoid bedbugs which can be present even in high-end places), a hot shower, wall outlets for mains charging to top-off my chargeable gadgets, running water, heat/cold to some degree other than what's outdoors, a TV -- usually with cable or satellite reception -- and a landline telephone with secure bike/gear storage (locked in the room) while I walk to the store for resupply of food and goods and haul it back in one of those little ping-pong ball-sized folding shopping bags Walmart offer for USD$2 apiece, complete with mini-carabiner to clip it to my HB bag loops for carrying when empty.
I leave from home with a couple weeks' supply of food, but beyond that, my on-road food costs are pretty minimal to near zero during that time frame (trip-food costs offset what I would pay at home, and I take it with me). I'm big on water, so that saves on soda costs; tea or similar makes it different when served hot at breakfast or dinner.
Longer trips are more costly, 'cos I will have run through my supplies past a couple weeks. I shop at outlet/bulk/discount grocery stores when I can if I pass them on the road. Farmer's markets yield a good spread, as does windfall fruit from trees and orchards (not trespassing into fields, but on the road shoulder and within reach from there). I'm not shy about checking out the dumpsters behind stores, in the cool of the morning, when bruised fruits are culled from the shop displays and are freshly discarded. My food costs dip precipitously on these trips 'cos I find I just don't eat as much, nor do I desire to. I do lose an even pound a day, on average.
As for daily foods, I like the Nile brand of cup-soups, though similar are available at about the same price. I throw away the foil top and paper cup and repackage them for freezer-bag cooking in a Reflectix cozy. They usually cost 88¢ apiece and make a meal if fortified with other stuff, like some shreds of beef or turkey jerky or a handful of dried veggies. Three of those a day make my base meals.
Don't forget fast-food places have ultralight plastic dinnerware and packets of salt, pepper, ketchup (America's version of tomato chutney), mustard, pickle relish, or red and green taco sauce in the lobby for free to tart things up, and they foil packets are temperature tolerant and need no refrigeration. I've bought enough of their regular food in the past without condiments to not feel any worse about picking up the occasional packet than I do about using their restrooms. Add in a scoop of powdered or loose tea for morning or evening, or a packet of hot cocoa, and I'm pretty well set.
In-between, I get a big bag of trail mix from warehouse food stores' bulk food bins -- like GORP (Good Old Raisins and Peanuts) with dried pineapple, apricots, almonds and such. A large sack costs about USD$5 and lasts me over the course of a week or so. Heavy, but a good staple in-between. I will sometimes buy a jar of Gatorade powder and use that in a mix instead of buying the expensive bottles of the stuff (why pay for the water that makes up the bulk of it?). Little alu cans of mandarin oranges, mushrooms, or vienna sausages (potted meats) cost about 50-75¢ apiece, and tinned tuna or chicken isn't too bad, but is protein. Day-old bread ("dead bread" in Danneauxspeak) never killed anybody, and that with a jar of peanut butter goes quite a long ways. When the loaf starts to go bad, I lay a few slices out to dry in the hot sun (remember, air temps are often 125°F/52°C where I go and ground temps are over 140°F/60°C, so it doesn't take long to dry bread on a rock. It doesn't exactly toast, but it stops it going stale as fast, and keeps mold in check (dry climate and the dried toast has less moisture to support a mold colony).
What's an ideal Danneaux dinner while touring on-the-cheap?
Some of the Nile Chicken (flavor) dried vegetable soup with a small tin of chicken breast and a handful of wasabi-flavored peas all boiled/steeped together in a freezer bag/Reflectic cozy gives me a meal fit for a king on only 8oz/.23l of water, 4 minute's fuel (to boil it) and 5 minutes' time after (to steep in the sack) with no dishes to wash (I eat out of the bag, propping it in my little anodized alu bowl). A handful of my trail mix for dessert, and I'm set till morning.
I usually awaken at 4:50AM, have broken camp and am on the bike by 5:30AM, and put in a good 20 miles or so to warm up before breakfast. Breakfast is usually a handful of oatmeal in another sack/cozy meal, with some of the trail mix mixed in and steeped in the bag with dehydrated milk to top it. The occasional energy bar makes up the rest of the mid-day foodie needs.
Jim, ongoing tour costs can be very minimal if approached in this way, even in America. If I was doing this in France, Belgium, or The Netherlands, I would hit the Aldi and Lidl markets and cobble-together something similar, as I did in 2008.
Hope this helps.
All the best,
Dan.