Off the wall thought, but what are the chances of an "F-35B-lite"?
Using the powerplant and main structural assembly, but de-specified to remove the costliest of the stealth aspects, cutting back on the advanced systems.
For instance if you removed the stealth coatings, user cheaper structural materials and used an off-the-shelf radar?
It wouldn't have the same capability - but it may have a better availability, lower cost, could be in service quicker through needed less development and could be a stand-in (and learning curve enabling) interim stand-in