Wanted: suggestions on how to implement subscription / recurring billing

Question

I would like to set up a premium subscription service for a PHP/MySQL based site. The site is Wordpress based, but highly customized and I'm not looking for a plugin solution necessarily. To oversimplify, I need to query the signed in user's subscription level (paid or free) and tailor the content that gets presented accordingly.

I'm looking for suggestions on how to implement the back end for billing/payments. I know one option is to use the paypal API, but I was wondering whether there are alternatives that I should also be considering. One thing I have noticed with many sites using paypal is that the experience is quite disjointed in the way one gets passed from the original site to the paypal site and back again. Is this just the way these sites have implemented the integration or are there better options than paypal from a UX point of view?

Also...

1. Have you used any tools / libraries / services that made this easier?
2. Do you have any advice on this topic in general? Gotchas, pointers, etc.

Finally, we're not a large corporation (yet), so a solution that could scale with us would be ideal.

Answer 1

Every payment gateway is different, and whichever one you decide to go with will provide complete instructions on how to integrate with the various features they offer.

PayPal is of course the only one that is not regulated by any governmental body, and coincidentally enough, the only one that makes their money by robbing people blind. Shouldn't be too hard to find thousands of horror stories if you look.