The cheapest property on a Monopoly board is Mediterranean Avenue. It is one of the two cheapest properties on the board.
Mediterranean Avenue is not only the cheapest of the Monopoly properties, it is also the first property on the board and can't be reached without passing "Go."
The cost of the property is a mere $60 and rent is only $2 for unimproved lots. However, if Atlantic is also owned and the properties are improved with houses or hotels, the rent can be as high as $250. Despite being low in cost, it is easy to make money on these properties because they are landed on regularly as people come around the board.