It's not sexist it's just life.
In reality women are more likely to be bought and for higher prices and rhe main customers are men. If anything its sexist to both.
I think it's important not to ignore the existence of realities just because it's "offensive" or "not fair". This is just what happens in society.
Remember that the manga is just following our societal standards and so rather than calling the manga sexist, its more human society which is.
Of course don't overlook that its sexist to men as well as most of the planet makes them out to be perverted rapists when in reality it's only a few (women even less so)
You probably know all this and I'm probably digging too deep and assuming ur argument but I get defensive when people are quick to call "sexism"
How can Yuiichi be worth 0 yen! Same with the other guys with lower values! That's sexist!
If Kokorogi can be bought as a slave for 200 million yen, for well (her totally not big tatas)... obviously sexual reasons, why can't Yuiichi!
What if you were a slave buyer in the context of manga that happened to have taste in young pretty orphaned boys with rotten personalities (as evidenced by an inhumane onslaught of yaoi)!
Ok I'm done here, I'm probably on a police watchlist now (⊙…⊙ )