Wow, that's self confidence. Paying someone for the homework problem feels semi-okay. But what if you have a no-moonlighting clause at your current job?

But asking to be paid during the interview seems too much, even though you could have spent 3 days of your life, traveling each way plus the interview day.

Asking to be paid during an interview seems too much but a 4-8 hour interview doesn't seem too much? The average interview length across all industries is 40 minutes. Asking interviewers to spend 4+ hours on the hope of a job offer seems a tall demand. I think asking to be paid seems a fair counter to what is otherwise a very unfair ask.