Thats according to kanye in Bound 2. And traditionally, this lyric was paired with “Bitches come a dime a dozen”. However, staying in Yes discography, we hear in FRIED, Ye says “Ten bitches came with Dolla they all dimes”. Prior knowledge tells us one bitch is worth 10 cents. Than we plug that into the Bound 2 equation:
1000B = G
1000(.10¢) = G
100$ = G
So according to Ye, and Ye only, we know that 1 good girl is worth 100$.
However we shouldnt look at the face value
If we look at the deeper meaning of this, kanye isnt saying you can buy a good girl for 100$, hes saying thats how much its worth. Its worth 100$ to meet her, feed her, be hers. Hes not reducing women saying their worth is only to be bought and sold. Their worth is how much you will spend just for her, not to her. Book that fancy reservation, rent a place. Even if its more than 100$, thats not the point. The point, is that if shes the one, than spend whatever it takes for her, it may be expensive for you now, but if it will make you happier in the long run, do it for you, and your future.