I think it goes for $249/mo but if you sign up through a shopping cart that's one of their partners (like 3dcart or Monstercommerce) then you get a $49/mo deal.

I would have to say that's the HackerSafe logo along with the BBB are the most common ones to find on online stores and visitors are getting used to these. And if you use a payment gateway like Authorize.net, Paypal or Google Checkout then it's definitely worth adding these to your site.