Agreed, is that even a valid excuse? And he "fell in love at first sight" with a high schooler walking alone at night... idk about you, but highschoolers usually have an "air" about them of youthfulness that's easy to spot on sight and it's not like the MC looks mature or anything. He doesn't look, to me at least, like his body could pass for an adult's. He seems like a small guy.
Even if they were both adults, it's such a weird and sleazy thing to do! Especially since overall it seems the manga is going for a cute, innocent vibe. "Oh my god, I think I've seen the person I'm destined to be with! I want them to love me, how can I make them mine?? ...AHA! I know! Prostitution. Prostitution is the right first move here."
Oh definitely, who thinks it's okay to just be like "let me fuck you for $300"?? Wtf?
All right dude, drunk or not I just gotta say - offering to buy sex with someone because you "fell in love with them at first sight"... is SO not romantic.