We too just completed a gift/wedding registry app. We're not offering it through the app store as it's very robust and requires custom installation. This version comes with full-service install and styling to match your site. Landing page: shopifyregistry.com.
Pricing depends on your specific needs but right now it starts at $5k for setup/training (definitely not for everyone we know). We'll be offering a scaled back lite version in the app store soon that will be a decent alternative to the full-featured registry.
