First, S&S and Surf will always be more expensive on board. There have been threads recently figuring out cost savings if D or D+.
You will get one 24 period free, being Diamond. Since your days you need internet will then be 5, count on the ship price being at least $5-7 more per day than pre cruise price. Since you won’t be able to have any access in port, unless you find a wifi spot, do the math. I think the pre cruise price will save you money, but not a lot.