Crossing out/altering words was one of his techniques to make the words more pronounced, the thought being that by obscuring the word or phrase, it actually made you pay more attention to it.
Basquiat, like a lot of the more contemporary artists, realized the insane commodification of art, especially in the 80s, and the irony and absurdity of creating work destined to be auctioned off to the highest bidder. Even still, 50K is a crazy amount for that.