When you're on your ship, bring up the Menu and use your bumpers buttons to get to the Operations Tab, and then the Stats sub-menu.
On this screen, in the bottom left. You will see the Assets heading. Here you can see your Net Worth. Which is comprised of the following: Balance, Battlemechs, Weapons and Equipment. Naturally, the more weapons, Mechs and Equipment you have, all adds up to the grand total of your over Net Worth. If you hoard everything you can find, this will not take you long. I'm currently halfway there, and have just reached Rank 8.