I think at these prices today, 200 might be too high as that is ~600 Steem out of the pool (450 to author). However, to send it into a loss (most offer around 10%) would only take a $20 clipping. 200 is a good place to start perhaps though.
As for the burn, what might be interesting is if there is an option on the bidbots where a user can select it and the bid will provide the vote, minus any potential profit (and perhaps a fee) and it will be automatically sent to @null. That way there is the profit burn and potentially an actual cost to advertise through the bot. If the post is worthy, it will make profits anyway.
edit:
If the post is worthy, it will make profits anyway.
if it is useful and adds value, the cost of advertising will be small in comparison to what it may earn.
True, I may readjust my number. With the current price, and if Steem dips any lower, I will need to readjust.
Yep, and if it goes up significantly - move up. It is hard to think in terms of Steem allocation but when Steem is at 10 dollars, a 1000 dollar post is only allocating 100 steem, unlike now where a 30 dollar post does the same.