Problem:
- Small organisation takes credit card transactions using a manual process.
- Many of these transactions are Diners and Amex.
- Paypal Website Payments Standard only takes Visa and Mastercard.
Options:
- Get a Internet Merchant Account with bank, a gateway provider and process as required.  Cons: Expensive, Two suppliers, two sets of fees before getting your cut. Pros: Fast, Instant, Dont have to hold onto cc details. Can take Amex and Diners.
- Find a much cheaper MOTO (Mail order Telephone order) or CNP (card not present) merchant account solution with a bank and either:
- get an SSL cert, allow people to provide details online, but process them manually.
- Use a slightly more expensive man in the middle to do the same thing (securely get your cc details via a nice nice api). Still cheaper than a Internet Merchant account, no per transaction fee or cut.
- Pros: Validate transactions before you process. Cheaper, esp to take Amex and Diners.  Cons: Still have to automate.
- Find an alternate gateway/merchant/secure page supplier that takes Amex and Diners. This page provides a comparison on some services but it is a little dated.