bazzer: Paypal? I think it costs 3% + 30c or something like that.
astrae: I have just been through this exercise for work. We are processing 1-2 transaction a month.
With Amex we have signed up as a merchant directly with Amex. We just submit a manual hand written voucher and send it through. Money is in our account the next day.
For Visa/Mastercard we have signed up with ANZ (we use them for banking) and use an automated phone service to do a manual transaction. We haven't done this yet but will likely be doing it next month.
For a few transactions a month all online services were very expensive.
timmmay: Paypal. Plus I'm pretty sure this exact question was asked in the past 2-4 weeks, a search may find a thread.
ubergeeknz: Also check out DPS. http://www.paymentexpress.com/Products/Ecommerce/DPS_Hosted
edit: pricing from $50/month up to 100 transactions, setup fee $150. But I'm pretty sure it will be cheaper than anything your bank can offer.