it is best to buy your ticket earlier - earlier booking will cost you lesser. You can also check this:
i used it before to get Yankees tix,they really have good prices :
http://www.ticketwood.com/.../index.php

There's a site called Stubhub.com. Or you could go see a scalper at the stadium.

You could always check Stubhub.com

I don't know about the Yankees, but the Cubs even endorse the site. People with season passes sell their unused tickets on there all the time.

The Yankee website always offers some sort of tickets. If there is a game that is sold out, try finding a different game...or if you really had your hopes of seeing that team, like the Red Sox, play the Yanks, then I would suggest waiting until the next season. They are never sold out! I've also heard Stub Hub.com was helpful, but I have never bought off from there.

Try finding a different game. Unless the Yankees games are all sold out, which could happen.

Or you could always by tickets from a scalper for an obscenely high price, but I wouldn't suggest that.