I don't think we could get more than a 6th or 7th round pick for car and maybe only a 6th if we send a 7th back, but i do think Carr arguably has more value for a team that thinks they are a QB away than most of those guys other than Darnold. And Carr would likely come cheaper than Darnold and was much better than Darnold up until this year. Of course, Carr isn't likely to waive his no trade clause and is more likely force the Saints to cut him if they want to move on.
But, as far as the other available QBs:
Darnold is probably a better QB so most teams would take him over Carr. But you do have to wonder if he can do it in another system without the WRs they have in Minny. He also may want huge money coming off of a great year in Minny until the playoffs.
Fields is all about potential upside that you can teach him to throw. So, he's a bigger risk than Carr.
Russel Wilson may be done, apparently brings some locker room issues, and may want more money than Carr. But, it's probably about a wash with Carr.
Flacco may retire and is many, many years from his Super Bowl form. I'd take Carr over him unless Carr wants crazy money.
Wentz though he technically has a SB ring only had that one good year and it was Foles that finished it off. I think Carr is just a better QB than Wentz.