Bnei,
I find a good combination is the WooCommerce plugin for WordPress marketing, and Edwiser Bridge for synchronizing with Moodle and providing single sign-on to Moodle.
The basic WooCommerce plugin is free. The basic Edwiser Bridge plugin is also free, but the single sign-on and other extras can be purchased for a modest fee. I always use the two together, but I believe you can use Edwiser along without WooCommerce.
Floyd