Dev costs only or dev costs plus marketing?
Unless we know these specifically, it's hard ot compare games this way.
True, and i have no idea. What we do know though is that Horizons devs costs was around 45M...... and based on what nintendo said of Zelda, it would be within reason to deduce that they are talking about devs costs too. the game has been in active development since before 2013 after all when it was originally announced and was to be released in 2015.
A good way to estimate the cost of a games dev is to look at the size of the team making it and/or the duration of active development. If in 2013 nintendo announced the new zelda, then went on to say it would be out in 2 years.... there is no way it wasn't in full development.