tourbillon, I've lived and worked in 3 Continents, Europe, S. Africa and lately here in the US.
I had one week's notice to get here and start work, I flew out of Heathrow Monday morning and started working the next Day in California, I didn't have a clue what I was letting myself in for, so of course I had to get a SS number, Driving Licence, open a Bank account all whilst working 7 Days a week but it was great, an adventure, although I must tell you moving to another Country is never how you think it's going to be....
For instance, after 2 weeks at work, meeting People and making Friends etc it was just like working anywhere else, I learned I had to pay x% in tax, SS, State Tax etc but I didn't care, I'm more than happy to pay everything I'm expected to. To me it's part of doing business, I've never felt like a Foreigner here and I think there's a special bond between people in the UK and US, plus I've never looked upon any American being a Foreigner, I'm a big believer in "when in Rome..." and if you don't like it, LEAVE...
Whatever rate you get taxed, whatever amount of Money you make it's going to be a great experience for you and your wife, Paris is one of my Fave Cities, in fact, I worked 60 miles from Paris for 6 months (At peugeot) another great experience....apart from the looooong wet/dreary winters over there which you never get used to....
The point of this reply to your OP is that it's hard to put a $$$ value on an opportunity like this, but that's just my way of looking at life....you'll be shocked at the amount of Americans living in Paris, you'll make a lot of new Friends, look at life from a different perspective...One thing I've learned to be true, and I don't know who said it but "You can never go home" . But go for it mate!! Just look at paying all the Taxes as part of doing business. Incidentaly, you should beable to find a blog similar to this directed at 'mericans living in Paris, people are always happy to give advice, just do a google on it..Bon Voyage and good luck!!