How do I make a piece of furniture NOT smell bad?

I bought an ottoman at Goodwill and it just smells really musty—not smoky—just really musty. I used a “pet odor remover” spray three times now and have used an outdoor strength vacuum once. Now it just smells like musty apples.

Any other suggestions?

p.s. preferably cheap… as you can read, I bought it at Goodwill (for $10) and I’m a poor college student!