The only option is to purchase a single full license of Fireworks for $299:
Click on the purchase button, and it will be added to your cart.
A word of warning, though: Fireworks development was stopped by Adobe in May 2013 - two years ago! There will be no new versions, support, or updates for Fireworks. Already there are compatibility issues on newer versions of MacosX, and the GUI will not scale properly on retina screens in Windows without manual (unsupported) fixing.
Unless you are desperate to work in Fireworks, consider other alternatives.