Sucuri Wordpress Security & Scanner
Sucuri WordPress Security & Scanner is a security-based plugin that promises a suite of features to allow customers to protect their WordPress sites.
The plugin is free and offers some basic protection, but the main point of it is to integrate with the Sucuri cloud based Web Application Firewall (WAF).
This differs from Wordfence in that Wordfence is an application level firewall, so running within the WordPress application, as opposed to Sucuri's cloud based WAF that would run on Sucuri's servers, and intercept traffic before it gets to your WordPress application.
Sucuri offers several different pricing plans based on both the efficiency offered and the breadth of features, starting at $199 per year per site for the plugin’s Basic package.
Wordfence has a single plan at $99/year.