One of the cities that has always been at the top of the most expensive city lists is Paris , which has very high prices on everything but in recent years has become a cheaper city thanks to the fact that prices have fallen and that there are many free activities, especially in summer.
If you are going to travel to the "City of Light" , I recommend you find out before about the many free activities they have so that you can spend as little as possible. In the metro there are a lot of posters with free entertainment and they also take out a newspaper once a week called Pariscope and in which there is a list of all the activities in the city (it costs less than half a euro). Take note of some of the free activities in Paris:
– Beaches : They are only in summer but they are wonderful, I was in one last year and I loved it. They are made on the banks of the Seine so you can find them almost throughout the city, in addition to there are also concerts and various sports. In the Bassin de la Villette, to the northwest of the city, they have one that they have put an artificial wave to be able to surf. A joy.
– Cinema : This is not free but there are very low prices in the Parc de la Villette cinemas where every night, except Mondays, there are original version screenings. In fact, in the Villette area there are many free and very cheap activities. 
– Museums : Admission is free in all the museums managed by the City Council, which are 14. They are open every day except Mondays and holidays and you can enjoy free museum collections such as the Le Petit Museum of Fine Arts Palais, Museum of Modern Art, Carnavalet Museum or the Jean Moulin Museum. You will only be charged entry if you go to one of the temporary exhibitions, although it is always a very low fee.