I use a system called aMember Pro. It has plugins for all of the major payment systems, including authorize.net (which is what I use). It also integrates fully with UBBT (for an extra $40) and will handle all of the signups, recurring payments, cancellations, and the like.
You can find more info at their site,
www.cgi-central.net. I've been using it for my site now for over a year and we are very happy with it.
