The "hidden price" is to get around MAP (Minimum Advertised Price) policies, specifically with companies that enforce them - Bose, Apple, Monster, Beats Audio, etc.
From Wikipedia on MAP policies:
Minimum advertised price or MAP (also known as resale price
maintenance, or RPM) is the practice of a manufacturer providing
marketing funds to a retailer contingent on the retailer advertising
an end customer price at or above a specified level. Such agreements
can be illegal in some countries when members and terms in the
agreement match predefined legal criteria.
For Magento - this is available natively in Magento Go:
Aheadworks has a Magento Connect module for this:
Magento Enterprise Edition has built-in MAP support:
In product detail admin:
In configuration settings System > Config > Sales:
Thanks to @davidalger for pointing this out.