As for the "buy" option, it's pretty easy to turn off - you can save a "quick settings" set of options and then select all your galleries, and then apply the "quick settings" to the batch of galleries. And when creating a new gallery, just pick that preset of "quick settings". This includes more than just the "buy" option, and also things like whether to show EXIF, and stuff like that.
The one thing you can't do is change the "quick setting" and then have all the galleries change automatically to match the setting.
(example: http://photos.michaeldehaan.net)
As for the "buy" option, it's pretty easy to turn off - you can save a "quick settings" set of options and then select all your galleries, and then apply the "quick settings" to the batch of galleries. And when creating a new gallery, just pick that preset of "quick settings". This includes more than just the "buy" option, and also things like whether to show EXIF, and stuff like that.
The one thing you can't do is change the "quick setting" and then have all the galleries change automatically to match the setting.