I honestly think they have a better shot at signing Iupati than Crabs at this point.
Crabs and his representation obviously value his worth a lot higher than the Niners do. I can see the Niners giving him a middle of the pack deal based off of his production since he's been in SF. I can see Crabs team wanting Top 5-7 WR money based off of his potential.
Honestly, Crabs would be foolish to sign any deal the Niners give him now. Even if he gets hurt or has a horrendous season, the deal they've offered will stay the same. His value can only go up.