2 very recent examples for you:
2007 Volvo S60 D5 2.4D Auto 185ps, 47 euros per month
2012 Renault Laguna 2.0DCi 130ps, 38 euros per month
The Volvo is a UK car I am in the process of registering in France, there is usually a bit of an extra cost because it’s right hand drive. No different in France to what you’d expect in the UK, insurance companies don’t like things that are a bit out of the norm. The Renault is a French registered car so nothing unusual about it. Clean driving history, no special requirements etc.
I had no problem getting the maximum 50% bonus - I just sent a copy of the latest UK renewal to my local agent. I am in Dept 37, I don’t know how that compares with your proposed area for risk rating. I possibly could have got cheaper cover via a direct internet based insurer, but that wouldn’t have been so easy to arrange. These are both via AXA, and the local agent was very helpful. Also, very few companies will cover a non French registered car, and those that do only do so on the basis it’s being registered here imminently.
A couple of things to bear in mind:
Insurance in France normally includes breakdown cover - in fact I haven’t found any way of buying insurance that doesn’t include cover, or any way of buying cover separately. Factor that into your comparison with UK prices.
Excesses are often a bit higher. The Renault excess is 450 Euros, compared to the £250 I used to have in the UK on the Volvo.
You haven’t said specifically whether your car is an existing UK car or you will be buying one in France. For either, you can get an idea of the cost of your registration (immatriculation) from several internet sources. This link is for the official simulator: https://www.service-public.fr/simulateur/calcul/cout-certificat-immatriculation. You’ll need to do a bit of research to answer some of the questions - eg fiscal power rating.
However you won’t be able to actually register it yourself until you can get access to the ANTS system, for which you need a France Connect ID, and that’s something you won’t be able to set up until you are in the country and have, for instance, a social security number. So you may need to pay a 3rd party provider to register your car for you. If you buy here, most garages can do it for you for a fee.