Your numbers are essentially right. Most hockey teams share the basketball stadium, though, and almost all soccer stadiums are shared. But stadium costs are rising: both the new Yankee Stadium and the new Cowboys Stadium cost over $1 billion.
However, what makes your numbers very conservative (in terms of overestimating public costs) is that few stadia are fully funded by the public. Most of them are partially funded by the team or the league.
(Amusing notes: Montreal's stadium, built for the Olympics and used by the Expos, cost 1.4 billion dollars, but .9 billion was in interest. The world's most expensive stadium, the new Wembley, cost 1.5 billion.)
However, what makes your numbers very conservative (in terms of overestimating public costs) is that few stadia are fully funded by the public. Most of them are partially funded by the team or the league.
(Amusing notes: Montreal's stadium, built for the Olympics and used by the Expos, cost 1.4 billion dollars, but .9 billion was in interest. The world's most expensive stadium, the new Wembley, cost 1.5 billion.)