Well even though Knox is in his last year of his rookie contract I don't think Beane will sign him up for an extension unless
Knox and his agent want to tie it up for a reasonable number. TEs usually go to the end of rookie contracts before signing.
As to his worth look no further than 2 FAs (Dalton Schultz, Mike Gesicki) this year will get $10M-$12M.
Guys like Uzomah, Njoku, Max Williams and Evan Engram will get $6M-$8M.
So, make your plans accordingly.
Personally, I don't think Knox is going anywhere. They will draft a TE around the 5th round this year.