Accommodation: There are many campsites and several secure parking areas for motorhomes in the Barcelona area but they are very expensive. A much cheaper option is to park in the free Aire at Colonia Guell. You could also visit Gaudi’s Crypt, the incomplete church which Gaudi designed for the village. (€9 including audio guide tour of the church and village).
Transport: Rather than catch the train from the closest station of Colonia Guell, walk 10 minutes down the road to Moli Nou which is within zone 1. A day ticket for the train and Barcelona metro system costs €7.60.
Sights: A lot of the main sights in the city are very expensive but it is possible to spend a day in the city without spending a lot of money whilst still seeing a lot of interest.
In the old town you can visit the Cathedral and its cloister for free. The interior is very impressive and the geese can be very entertaining.
The remains of the Roman Temple of Augustus are well hidden by the surrounding apartment blocks but, if the door is open, they are worth a glance.
The courtyards of the Casa L’Ardiaca and the Frederic Mares Museum are very beautiful and free to enter.
Boqueria Market is a riot of sounds, smells and sights. The fresh food on offer will make you salivate and if you are lucky you can dine out on a few free samples. If not, then there are plenty of bars and food stalls around the market to keep your stomach happy.
Placa Reial and Placa de Sant Jaume are good places to soak up the Spanish atmosphere with a coffee or a beer.
Get some exercise by walking down the busy La Rambla to the port or visit the Parc de la Ciutadella where you can marvel at the many sculptures, the huge mammoth and the cascading fountain.
Close to the park, the former Born Market is now a cultural centre with exhibitions (some free). Recently they have uncovered the ancient city beneath the foundations and it can be viewed without paying. There is also a very nice café / bar if you need refreshment and a bookshop to nourish the mind.
Many people visit Barcelona for the art and, while it is expensive to enter many of the wonderful museums and houses, it is free to gaze at the exteriors. There is a good value Art pass and some places are free to visit between 6pm and 9pm on Sundays.
Lunch: Avoid the expensive restaurants and cafes on La Rambla and in PLaca Reial and take a few steps into the side streets for a better value meal. I ate at La Crema Canela, at the entrance to Placa Reial. 3 courses, bread and a drink for only €10.45. Good value meal and speedy service but cold plates and small portions.