It wasn't nothing at the time. $7million was a lot of cash back then. And the Americans mocked the idea. They called it "Seward's folly" and thought it was a ridiculous waste of money. Seward was the (US Secretary of State). They also called it "President Johnson's polar bear garden".

In hindsight, it was a good deal for both parties. At least Russia got the money because it really is true that Great Britain would have annexed it for themselves. It is the only reason why the Americans were willing to pay what they did for it.