#1 pick slot is 4m. It decreases by 90k be position.
R2 + R3 is 1m
R4 thru R10 is just under 1m
R11 thru R25 is about 150k
So, if you had 1st pick, you need just over 6m. 24th pick will require around 4m.
You can check previous drafts for slot money cost in the first round if you don't want to do the math.