As ever, this is relative to a multitude of factors but if you use the basic shopping basket (or cesta basica) which is used throughout Brazil then you will at least have a clearer idea.
João Pessoa is one of the cheapest cities to live in at the moment.
However, living beyond the basic shopping basket can be a bit more expensive. For example, if you can’t do without a particular product from your home country then that will up the costs a little, especially if you buy it here.
Procon (Dept of consumer protection) regularly publishes charts which show you the most economical places to buy your fuel and food. Similar surveys are provided for white goods (domestic appliances) and the recent removal of a type of tax has also had a big impact on prices.
Considering the city’s location there never seems to be a shortage of anything particularly fruit and vegetables (allowing for seasons).