Great news for us and a very good choice for him. I see Fields as someone who might be on the "Parker Plan". If he left this year, best case he would probably be taken in the 3rd or 4th round, but if he stays and has an outstanding year next year, he could end up in round 1, like Devante Parker did.
With the way the NFL salary cap is structured, first round picks get a large majority of the money under the "rookie salary cap". After round 1, the salaries are a lot less and all very similar for rounds 2-7.