Answered 8m a day?

I've actually been doing this lately, and while it's not astronomically profitable, it can make a tidy sum due to the clues being so quick to obtain and solve. Think about 6-8 clues an hour, with around a quarter of them giving a unique treasure trail reward (excluding biscuits and teleports). While I haven't sold anything I've received from my clues (I'm a fan of stockpiling clue rewards) I would estimate anywhere from 500k-1m an hour depending on how many clues you can do an hour and obviously varying wildly based on rewards.

And for the record, I've found the fastest way to obtain level 1 clues is by thieving the HAM members in their hideout near Lumbridge.