The price has to be reasonable
What's reasonable? The general consensus around the NFL is that the asking price will start at three first-round picks, plus. But that's only the start. What if the Texans want all four of the first-rounders the Jets have in the next two drafts? What if they want Quinnen Williams, too?
There's a theory some have that you can never pay too much for a franchise quarterback, but of course there'll be a line somewhere. If they Texans really don't want to deal Watson they can set the price obnoxiously high so no one will pay it, and then tell him that they tried.
And remember, Jets GM Joe Douglas wants to build through the draft and there are indications he thinks he can build a winner around Sam Darnold. He's not going to give away every chip he has if he thinks he's got a good quarterback who can be a winner if he's surrounded by a better team.
He has to convince the Texans to do it sooner than later
The deadline for this deal is probably April 29, the first day of the NFL Draft. Surely the Texans will want picks in this year's draft in return and they'll need to know if they have to draft a quarterback.
More realistically, though, the date is March 17 -- the start of free agency -- especially for the Jets. They're going to be players in the free-agent, wide-receiver market -- and you can bet those top wide receivers are going to want to know who'll be throwing them the ball on their new team. Plus, the Jets will want to know if they still have the high draft picks to fill any of their other needs, or if they'll have to spend big at other positions, too.