In the SFBA, nobody is asking for $500 million; instead, the owners are looking at putting up around that much.
IMSHO, it all depends on cost. If I were in SF, and the 49ers were going to spend $600 million on a new stadium, and wanted $100 million of city money (e.g. to pay for road improvements), then I'd vote yes - it's worth it. But $500 million for a basketball arena? No way!
--Tony