I wish I knew :) I think the only ones who can answer this question are the bid bot owners. I think a good starting point is 5-10% of the bid amount goes to the bot owners. I got the figure from Minnowbooster's delegation deal where it has a facilitation fee (of around 5-10%).
So a big whale bot like Appreciator that has a vote value of around $500 SBD could be getting somewhere around 50 SBD per voting round. Again, this is purely speculative from what little I know about the bots themselves. Assuming everything is automated, 50 SBD every two hours is pretty damn good.