£35 - £40 a day will get you transport (buses at least), lunch in a pub with a few drinks and an inexpensive hostel or campsite. If you go as a couple, stay in budget b & b´s, visit a few tourist destinations and eat in a mid-range restaurant, a realistic figure is £60 each per day.

Average prices:
Loaf of bread: 80p
Litre of milk: 70p
20 Cigarettes: £5.00
Pint of Beer: £2.00 - ££3.00
Meal: £2 - £5 (Budget), £5 - £15 (Mid-range), £15+
Lodging: £12- £18 (Budget), £18- £50 (Mid-range), £50+