Here are all NFL running back current 2019 league year contracts in a sortable table -- 400 hundred players from Elliot and Gurley down to practice-squad guys.
Kamara can actually get a top-several deal without breaking the Saints' cap. Look at the column Guaranteed at Signing -- that carries more sway than Average Salary.
Given that, I look at Devonta Freeman's and Leonard Fournette's contracts (fourth and eighth on the list at the link). Compared to each other, Freeman's base salary figures per year are higher while Fournette's signing bonus was much higher. Also of note is that Fournette's entire contract is guaranteed -- he gets paid everything even if he's released or injured.
Seems like it would be a fair offer to slot Kamara between Freeman and Fournette somehow. It would be somewhat risky to fully guarantee Kamara's entire deal, but doing so might be a way to mitigate the cap hit and convince Kamara's camp to accept less than the "fluffed up" total contract numbers gotten by Elliot, Leveon Bell, and Gurley.