Petsmart.com has the Solvit Extra Large PupSTEP Wood Stairs on sale for $54.99 after instant savings. Add them to your cart to get the discounted price. Amazon.com has the same set of stairs for $97.
These stairs are designed to support over 200lbs and can be folded down for easy storage. They're designed to help your pet reach places but arguably could be used by humans as well. Free shipping.