@Stu
According to
GratosTEL - VoIP-in DID Betamax Voipbuster, Voipcheap and some forum reports Betamax stopped assigning French DIDs back in 2007.
$5 a month is kind of expensive.
@migelli
I can't find any information on French numbers at Eutelia.
Anyway I found
ippi, who provide free geographical DIDs, but only to "résidents en France métropolitaine" and they seem to do some geographical IP-lookup, so I can't register with them at least at this very moment, but I'll find a solution.