You can have a look at our cost of living calculator (you don't have Seattle but you can choose other cities in the US).

I would say that an equivalent salary is ~€100k, which is very expensive in France (probably a Director level, in a big company). I quickly looked on http://www.monster.fr/ for "Architecte applications logicielles" in "Paris" and it gives jobs 50 000,00 € - 65 000,00 € /year

 

Yes it is expensive, especially accommodation if you want to live in the centre. Ranging from €800/month for 20 sqm in some areas to a 2 double bedroom flat for €1500 for instance.
As I said, you will also probably earn less as your salary in the US is equivalent to a top position, while IT architects can expect probably 20-40% less... again it depends on the sector and the job.