They've admitted it costs more to do so than not doing so, and the benefits (in thermal reactors) are limited. The value of separated Pu in MOX fuel is actually negative (it's cheaper to use freshly enriched uranium), and MOX fuel cannot be recycled again in thermal reactors due to build up of undesirable Pu isotopes. France has terminated their fast reactor program, which had been the actual intended use for separated plutonium.
Interesting. Are you talking of monetary cost or energy/raw material cost? If it's the former, that might be very dependent on market conditions.
Monetary. Uranium would have to be greatly more expensive to justify reprocessing for MOX for thermal reactors (or for fuel for fast reactors, for that matter).
France has recently increased its prices on nuclear power. I noticed earlier last year that Germany is importing nuclear power from France, which is subsidized by France. So, and take this with a grain of salt, I am not an expert on this topic, Germany was essentially taking advantage of France. It is possible that they have now fixed this through the price hike.