The cheapest way is to use public transport in the form of local vans called Alugers. The departure point is close to the roundabout opposite the BCA bank in Santa Maria. The price is 1 Euro or 100 Escudos from Santa Maria to Espargos, but remember the van needs to be at least 3 quarters full before they leave and they will keep beeping their horn and calling out their destination until they have enough people to go. Taking the Alugar can be a fun experience, and you may meet up with like minded independent travellers. It’s certainly the cheapest way to travel but not the fastest.
It is important to use only licensed taxi drivers. The cars are light blue with a yellow horizontal stripe, and make sure you get the price before you depart. There is an official price list for journeys, for example from the airport to Santa Maria. Currently This will cost you 10 Euros or (1000 Escudos).
The price from the RIU hotels to the centre of Santa Maria is 3 Euro (300 Escudos) or 4 Euro (400 Escudos) in the evening, you can then base other journey costs on these prices.