I’m on Enbrel, plus MTX and a multitude of other drugs and it costs me about 4euros a month… diseases like RA are classed as affections longe durée (ALD) so your costs are covered 100% once you are in the health system. So if you are french resident, and join the health system, and find a hospital based rheumatologist to provide the prescription then no problem at all.
If you are covered by some type of insurance rather than being in the french health system then I really don’t know - sorry! I guess it depends what you mean by insurance, as some I know won’t cover chronic or pre-existing conditions. All I do know is that the Enbrel itself costs 760 euros a month, so whoever’s providing it for you in the US is paying or charging over the odds!