Successfully complete your first season in Franchise mode. When you
begin the next season, there should be some great free agents that can
be acquired (for example, Cliff Lee, David Ortiz, Torii Hunter, etc.).
However, when you try to sign one, you may not have enough funds. To
bypass this, go to "Manage Roster", select a player, and go to "Edit
Player". Scroll until you find "Contract". This will show their current
contract (for example, $1.4 million and 4 years) and each year's salary.
It also gives you the option to decrease or add a year, or even drop his
salary very low in the final year, etc. For example, as the Cubs select
Lee, max his contract out to ten years, and set it to the lowest amount
on each year ($300,000). Save the game, then go back to free agency.
Sign Torii Hunter, and you should have more money available. You can
repeat this with as many players as desired.