I'm getting charged 100k a week. Since the max rental amount is 50k, why am I getting charged double?(is it because i'm KOS?).

hopefully yes (nothing personal Knauf) a respected player should be charged less than a kos player
if this is how it works its a good idea if its not it should be

Due to a conversation with Phaserlight, I will include this from a screenshot:

Hm, yes, it is because you are KOS. There are modifiers based on your faction standing with the station.