The GoCardless gateway allows you to take payment by Direct Debit (in the UK only at present, but might open up to other countries soon). This is probably the cheapest way to receive funds as you only pay 1% per transaction with no other fees whatsoever. There is also no issue with card expiry dates, and if a client gives you pre-authorisation, you can debit their account to take payment for invoices whenever you like without needing approval for every transaction. It also supports one-off and recurring payments.
For £50 free credit toward GoCardless transaction fees, sign up for a new account using this link
This gateway has features in addition to the normal nBill activities such as paying for orders, quotes, and invoices. After installation you will find new menu options in the Extensions menu which allow you to invite your clients to set up pre-authorisations. You can see who has been invited, resend invitations, or send new invitations, and amend the wording of invitations. Those that have set up pre-authorisations can then be debited for any outstanding invoices. You can also take partial payment of invoices if required.
Please note: unlike other payment gateways, payments with this gateway take a full 7 days to clear. Orders will not be activated and invoices will not be marked as paid until confirmation arrives that the payment has cleared (although you can configure it to process orders immediately, but you then run the risk that the payment might fail - for example if the client doesn't have enough funds in their bank account - in which case your nBill records may be incorrect). It therefore might not be well suited to selling products for immediate delivery.
This is an nBill extension. Use the extension installer in nBill to install it.