It's not that he needs the money. Although he supposes his dad will probably disinherit him when he hears, and then he'll need some money.
It's not that he wants to marry a billionaire, in particular. There are probably people who kink on that but Lee isn't one of them. It's just that he doesn't have a better idea for what to do with himself after college, so he figured he might as well horrify his father and stepmother by trying to find a man to marry as fast as possible.
Billionaire Marriage Brokers isn't the only agency he's signed up for, but it's the one with the most rigorous selection process. So...probably the safest?
He can tell himself that for now, anyway.