DoD Buzz has the latest on the alternate engine. The story notes that the backup engine program currently has a "$30 million a month burn rate" but only 52 hours of testing complete on product-configuration engines.
Pratt & Whitney’s F135 propulsion system powers the new advanced, single-engine tactical fighter, the F-35 Lightning II, developed by Lockheed Martin. The F-35 has unique capabilities for conventional takeoff and landing (CTOL), carrier-variant (CV), and short takeoff and vertical landing (STOVL). The same F135 engine will power all three variants. Visit http://www.f135engine.com to learn more.