Peru isn't the cheapest destination in the region but it is possible to discover the country for a reasonable price. Don't forget to check the exchange rate between the dollar and the pound. The Peruvian currency, the sol, is tied to the dollar and the cost of your stay can therefore be subject to variation.
Even though you'll find cheaper destinations in Latin America you will realise when you get there that your trip to Peru won't be too expensive. The situation still changeable nevertheless and you must take into account the ups and downs of the dollar since the Peruvian currency is linked to it.
As regards day to day expenses, this is the area where you can make most savings. Peru is a country that has adapted itself perfectly to tourism by developing its infrastructure to welcome visitors. You will therefore find a whole range of hotels and restaurants from the very basic to the most luxurious. There is something for all budgets. It's up to you to choose depending on the level of comfort you are looking for and according to your means.
It's the same for public transport. Travel within the country is usually by bus and here too the rates depend on the level of comfort chosen. The journeys are sometimes very long so this is an expense that can be quite considerable it you move around a great deal. On the subject of transport, here's a little aside about the train that runs to Aguas Calientes for those visiting Machu Picchu. The price per mile is, in fact, the most expensive in the world. It's a real racket, in that the train is presented as the only means of getting to the famous Inca monument. This is completely untrue. By changing buses at Ollantaytambo and Santa María then walking a little, you can save up to 500$, about £350. You can even go for free if you walk alongside the railway line from the outskirts of Ollantaytambo. A stiff hike of 28km, or about 17 miles, but wonderful too.
To stay in a double room generally costs between about 50 et 200PEN (10 to 50€) according to the level of comfort chosen. Bear in mind that the rates are a little higher in Lima and near to the tourist towns and sites.
To eat, if you choose a table in one of the little canteens on the markets you can have a full meal from about 10PEN (£2). In the more classic restaurants, the prices start at 16PEN (4£) for a main course and prices can be similar to those in Europe in the very touristy areas and even more so in the best restaurants in Lima.
As far as transport goes, it's the same. It all depends on the comfort level and the distance. To the 150PEN (£35) price of entrance to Machu Picchu, you have to add the rip-off price of the train ticket. If you have time to spear and you are fit enough for a little walking, boycott it.