Almost all of the scripts will work with Paypal, although I could never get whois.cart to log in and make the connection correctly. But I'm impatient with configuration items that are cumbersome.
For recurring billing in Paypal, use "Subscriptions" as the sales type instead of "products". You can have static web pages with a "Subscribe Now" link (you can rename the link if you like) and Paypal takes care of the checkout process.
The automated scripts we are talking about here are intended to handle the entire sign up process ... allow the customer to sign up, buy a domain name, select a web package and pay for it all. Then the script creates the web account for the customer, gives them the password, and the customer is set to go.
The problem for very small companies, like mine, is that I'm not sure I want it that automated. Almost all of my customers are people referred to me for set up and other consulting type of work. A charge back on Paypal is pretty expensive. And when I had a sign up form that looked like it was an automated script, it attracted thousands of spam submissions from Chinese hackers; some of them put a credit card number in the comment field (I'm sure it was a stolen card number).
Not all of my customers pay by PayPal ... I accept personal checks from 4 of them. One pays me every year, others are on 6 month intervals. For them, I'm using a PC based freeware invoicing program that allows recurring invoices (hard to find under $200.)
BTW - I forgot to mention that Dathorn has ClientExec licenses for $4 a month as an add-on to your account here. Not sure if there are limitations on that in terms of how many customers you can manage through it or not. Maybe Andrew will chime in here.