As detailed across a series of articles on ESO's support website, some of ESO's computer players are eligible to buy a digital copy on console for $20 (€14.99 or £12.99). To do so, you need to have purchased and registered a PC/Mac copy by no later than June 30, 2014. If you did that, you have from now through May 9 to visit ESO's PC/Mac store and purchase the discounted version, which is available under the long-winded name of "The Elder Scrolls Online: Tamriel Unlimited for Console with account copy."
Buying this will get you a full digital copy on your choice of Xbox One or PS4, no different from the version you'd be able to buy from the respective consoles' online stores for $60. Once you've purchased this, you'll receive a key and instructions via email sometime ahead of the console game's launch on June 9.
Also as part of this process, your account will be copied to the console version. It's important to note that your account will literally be copied--it isn't simply being moved, meaning you'll be able to continue playing on computer after your account is copied. However, your progress between the two platforms (or three, if you pay to be transferred to both consoles) will be separate from one another after the copy occurs, a date for which has not been set.
The transfer will bring your characters to consoles along with their gold, inventories, and bank inventories, but a number of things will be left behind:
Raid leaderboards status
AvA leaderboard status
There's no word on whether console transfers will be made available for those who have bought ESO since the end of last June.
ESO: Tamriel Unlimited marks the game's long-awaited console debut. It won't require a subscription fee (outside of Xbox Live Gold or PlayStation Plus), as has been the case with the computer version since March, but it will offer an optional subscription and other ways to keep spending money on it.