If you're interested in buying a minor-league team, here are some figures for you, from the official Minor League Baseball site:
An entry-level team, playing in a Rookie League, will get anywhere from $650,000 to $1.1 million.
Stepping up, a Class A Short-Season team costs at least $1.8 million.
Single-A baseball is a little more pricey - we're talking between $2.5 million and $5 million.
Teams from the AA Leagues go from between $5.5 million and $8 million these days.
Finally, if you want to bat with the (sort-of) big boys, you can buy yourself a Triple-A team for a cool eight to twelve million dollars.