It seems the British influence in the country still reaps rewards for the UK traveller. In all cases the fee for the stamp is five dinar, payable on the spot. If you are not from one of these countries, you will have to make the necessary visa arrangements before boarding the plane.
Gulf Cooperation Country nationals do not need a visa to enter. Conveniently, Bahrain now has an e-visa system which allows for the purchase of the necessary tourist visa online by credit card and is subject to an additional two-dinar processing fee.