The cost to rent a home in Portugal depends on several things such as the size of the property, whether it is furnished or not, whether it has a pool or not, and whether it is with a garage or without. It is really relative.
As an example, in Cascais, a two-bedroom, furnished apartment without a pool would cost around €1,200 (US $1,300 or £865). The same apartment but unfurnished would be about €800 (US $870 or £587). If it has a pool and a garage, it would go up to about €2,000 (US 2,180 or £1,450). You pay for the utilities separately. The rental contract would be for one year.
The further away from Lisbon you go, the cheaper everything gets. Cascais and Estoril are the most expensive towns in Lisbon. It is even more expensive in Cascais than in the Algarve. Cascais and Estoril are the Beverly Hills or the Park Lane of Lisbon. Estoril is where the ex-kings live, such as the previous king of Spain, and most of the previous kings of Europe.