Oakland A's roster mistake
On the Oakland A's default roster, notice that they have Milton Bradley, Antonio Perez, and Andre Ethier on the team. This is incorrect because the Dodgers traded Bradley and Perez to Oakland in exchange for Ethier. Therefore, all three players cannot be on the same team.
Signing a created player cheaply
You can edit any player and their abilities, and not just the way they look. Sign a desired minor leaguer to the maximum term (seven years) at the lowest amount, even though they may get upset later in their career. Then, change their name, abilities, position, etc. This also works for changing other major league players. For example, you can change Joe Young on the Giants to Barry Bonds by editing everything except his appearance. By doing this, you can sign an entire team. Note: You can only re-negotiate contracts at one year to seven year contracts at about $1 million each or less, then make them perfect. When you are finding a player to make your own, look for one year contracts.
Bouncy ball...