What is the safest and cheapest legal way to send money to Bangladesh from Bahrain?

Use a licensed exchange house or a bank, never hundi. Licensed exchange houses in Bahrain are regulated by the Central Bank of Bahrain and give you a receipt and a tracking number. Hundi is illegal, gives no receipt, and you can lose your money with no recovery. When you send through a legal channel, your family in Bangladesh can also receive the government's 2.5% cash incentive on the amount. To send, bring your CPR card. Compare the rate and fee at a few exchange houses, as they differ. Keep every receipt. Sending money legally protects it and builds a record of your income for other official needs.