And how much does a Source (HL2) engine license cost? Probably several hundred thousand $
Valve negotiates each license separately, and there have been a few indie Source-based games. Zeno Clash and Garry's Mod come to mind.
I would expect the terms to involve a cut of each sale instead of a flat rate.
+ Time for recreating the full game beside textures
Well, textures and models anyway.
KF would have probably been released in the Year 2011 and would have cost 40$.
I think it would be more likely to be released late 2009/early 2010, and I don't think the price would have changed.
All that just because you don't like the flash light.
There are several strong benefits to the Source engine. The materials system, the ragdolls, the particle system, the rendering system, the far better voicecom, multicore support, the scripting engine, higher entity limits, better netcode, etc...
The source engine is far more advanced than the U2.5 engine, which is more the result of Valve's constant work on it than anything else. Of course, that itself means that a source-based KF could be designed to let Valve's engine improvements migrate into the game over time.
However, I don't think TI wants to go down that path at this time. Maybe they could go engine-shopping for KF2, but the game's recent launch gives them far more pressing matters to deal with.