Listed below are the points needed in each level to get the S Rank. Keep in mind that these points include the bonuses you get on the results screen, which is why the requirements seem quite high at first.

This is particularly useful for 100%, and I might consolidate this into a 100% guide on this SRC page in the future.

Lost Valley: 950,000 Spaceport: 1,400,000 Ghost Town: 900,000 Prison Hall: 1,050,000 VS. Zavok: 1,250,000 Egg Gate: 1,200,000 Arsenal Pyramid: 1,450,000 Luminous Forest: 1,100,000 VS. Infinite 1: 980,000 Green Hill: 900,000 VS. Eggman: 950,000 Park Avenue: 1,150,000 Casino Forest: 1,000,000 Aqua Road: 1,050,000 Sunset Heights: 850,000 Capital City: 1,250,000 VS. Infinite 2: 1,000,000 Chemical Plant: 900,000 Red Gate Bridge: 1,150,000 Guardian Rock: 1,350,000 Network Terminal: 950,000 Death Egg: 1,150,000 Metropolitan Highway: 1,050,000 Null Space: 1,500,000 Imperial Tower: 950,000 Mortar Canyon: 950,000 VS. Infinite 3: 1,200,000 Iron Fortress: 1,100,000 Final Judgement: 1,100,000 VS. Death Egg Robot: 2,000,000