By Katherine NoyesWith the prospect of a collective $18 billion in revenue a year as motivation, it’s no real surprise that new digital subscription sites pop up all the time. Recently, however, a particularly interesting example caught our eye.Namely, Politico last week announced that it’s launching Campaign Pro, a new vertical subscription site aimed at political, PAC and campaign professionals.”This will allow us to go much deeper, cover exponentially more races in granular detail and write bigger pieces with even richer reporting and data,” wrote Jim VandeHei, Politico’s executive editor and cofounder, in a staff memo.With the new service, Politico will “have more people covering more races than any publication in the country,” VandeHei noted. It will also allow readers to zero in on the races they care about most and get related stories pushed to their email. Unique polling and polling analysis will be part of the service as well.Even more interesting from an industry perspective, though, are VandeHei’s thoughts on the big picture: “Stepping back, this is a great example of how our business model works. We can produce a product that is absolutely essential to a paying audience — and then utilize that team and coverage to write even stronger, better informed stories for our broader audience on the main site.”As we noted last fall when Politico acquired Capital New York, charging a target audience for “need-to-know” information can be a solid strategy — one the company is now testing with its $5,990 annual subscription pricing for the rebranded Capital service.Also working in Politico’s favor, though, is that B2B subscriptions tend to get impressive retention rates, especially when sold on a group or site license level; we’ve already seen that Politico Pro, for example, gets about 96%.No word yet on Campaign Pro’s pricing, but we’re betting it won’t come cheap. For more on pricing new subscription services like this, check out our related Special Report entitled, “How to Pick the Best Pricing for Your Subscriptions or Memberships.” If you’d like to know more about selling group subscriptions, Subscription Site Insider has a toolkit here.