At launch Golden Mario will cost you $12.96, however it remains to be seen how many will be available at launch. Other characters such as Marth, the Villager and the Wii Fit Trainer are no longer being produced and as such are rare, as well as Diddy Kong recently becoming rare as well.
Nintendo had this to say about the launch:
“Mario has always been golden in the minds of his fans. On March 20, Nintendo will launch the Super Mario Amiibo—Gold Edition, a shiny gold-colored Mario figure that arrives on the same day as the Mario Party 10 game for the Wii U console. The Super Mario Amiibo—Gold Edition will be sold exclusively at 3,000 Walmart stores in the U.S. at launch at a retail price of $12.96.
The new gold-colored Mario amiibo is compatible with multiple games that support amiibo. For example, Mario Party 10 features a new amiibo Party mode that players can only access by tapping their compatible amiibo figures on the Wii U GamePad controller to customize them and bring them into the game as board pieces.”
Recently releases such as Rosalina, Lucario, Meta Knight, and Shulk have also sold out in a short amount of time with being exclusives at places such as Best Buy and Gamestop, so fingers crossed Nintendo have shipped enough for people to buy.
No word as of yet if Nintendo plans to release the Golden Mario Amiibo in other places other than the US but if anything develops we will keep you posted.