On my recent JOGLE, I had to keep my costs as low as possible, so had to camp most of the time. I had 20 nights in camp sites which ranged from £5 to £18 a night, 1 night at my brothers in Taunton so free of charge, 1 night in a B & B at £28 and 1 night in a hostel at £25 making a grand total of £235 for accommodation. Of course you could wild camp in Scotland especially, so you could reduce this even more. I actually paid less than this myself as several of the camp sites did not charge or gave me a lower rate as I was cycling for charity, but I put all this money into the Air Ambulance pot.
The train fares were Gillingham Dorset to London , £11 London to Inverness £61 and Inverness to Thurso £12 making a grand total of £84.
These trains were booked 12 weeks in advance to get the cheaper prices and again I could have got the London to Inverness cheaper on the sleeper if I had got on the computer slightly earlier and picked up one of their bargain berths starting at £19 but you have to be quick to get these.
So as you can see my holiday of almost 3 and half weeks only cost me £319 for accommodation and travel to John O Groats. I was lucky enough to have friends pick me up from Lands End or that would have cost me another £60 in train fares. As far as food was concerned I tried to keep it to around an average of £10 a day, but this proved difficult. Breakfast was usually porridge, so just bought pint of milk each day for coffee and breakfast. Often bought rolls and cheese for lunch, or meal deals from Tesco/co op (sandwiches, pork pies and a drink - around £3) and then ate out cheaply or bought food to cook at camp site. I probably spent nearer £12-£13 per day average, but I did not really keep track of this.
So really the trip can be as cheap or expensive as you want it to be. I tried to keep costs low, but would still treat myself occasionally (like the giant ice cream costing £3.95) or the numerous cakes along the way. I did look into B & B but I could not make it financially viable for me.