I highly doubt this makes any financial sense.
The marginal cost to kill or seriously wound a Russian is probably something like $50k; the _entire war_ has only cost ~$250k per Russian casualty in direct military spending, and that includes lots of pricey defensive spending like anti-air defense. Ukraine has constantly been short on things like drones and ammo that could easily be purchased if only more funds were available.
I _highly_ doubt the French government is spending less than $50k per Russian. There's a ton of work that needs to be done to vet defecting Russian soldiers given the high chance they're infiltrators, and every failure is incredibly costly. That's on top of ordinary refugee expenses like welfare and other social support, which cost thousands per year.
Just spend the money on weapons and focus on killing Russians efficiently. The ones who are deserting were probably not effective soldiers anyway.
