A Bacs payment is the cheapest way to send payments. It only costs a few pennies, mostly depending on the volume and the bank, or Bacs bureau. When sending say 1,000 plus payments monthly this should be less than 10p, also watch out for hidden bank charges such as:
Find out here about bacs payment times
Bank to bank payments can also be made through CHAPS and the Faster Payments system. CHAPS are same day payments for high value transfers which cost about 20-30 pounds per transfer. Faster Payments are instant payments up to the value of 250,000 pounds per transfer, much cheaper than CHAPS.