I\'m trying to research how to add a subscription based pay model on an existing site of mine, but am running into a lot of conflicting information and caused me to be a bit los
One other potential option is to hit one of the other recurring billing capable gateways like Authorize.net or BrainTree. I don't normally suggest Authorize.net because of their slightly gimpy development process (you have to request a test account if you want to do continual testing which takes about 2 days) but I've done integrations with them on several sites and it works reasonably well. Though they do have the same inane policy as PayPal of naming 19 products which all seem to do what you need but don't in reality.
The only bonus to this is that people don't have to be PayPal members in order to do the payment and I believe Authorize.net has lower fees but that may have just been our accounts; our sales guy was a killer negotiator.
active_merchant and the SaaS Railskit both support Authorize.net and BrainTree.
I wouldn't recommend buying the Railskit just to look at quality code that uses active_merchant though, I'm certain there are other places that you can look for free. Railskits are really designed to be used as a base and it's almost guaranteed to have a different set of assumptions about setup than you had planned on so if you've made it anywhere on your project merging the two would almost certainly be a pain. On the other hand, if you're still just starting the site the Railskit might well be a great way to start over with a really sane environment.
We're also developing a subscription based site and this looks pretty interesting - http://chargify.com/. Could save quite a bit of coding time.