JFH who is the top paid prop in game is reportedly on 875-950k depending on source but let's say 875k, which is 1.1m under the increased cap.
Haas is IMO easily better and I'd happily give him 950k under the old cap which is 1.19m or round it to 1.2m.
I think the club will offer him something like 1150+ he will have some 3rd party deals for sure and could probably make 1.3m a year comfortably. Add on 100k in origin and rep payments, his overall earning potential is around 1.4 maybe higher depending on 3rd party sponsorships, if he keeps clean off the field he has Superstar potential there.
So even if France are offering 1.8m that's not a huge difference given he has no profile there and would likely make close to 0 in outside endorsements, not to mention living in France away from family and comfort zone. France's top tax rate is about 3% higher too, so that 1.8m becomes 1.75m.
If we're then talking about after tax net income, the difference is at most 200k a year. It's a bit but hardly worth changing country for, and that's before we discuss potential future earning potential he'd lose by going to an obscure league.
I think with the increase in the cap, outside leagues would have to be offering top players 2m and over to be seriously tempting.