I use an example of $0.01 in these mock adverts but considering this mechanic allows greatly boosts user engagement (ie advertisers are pretty much guaranteed those ads are seen by humans), highly targeted adverts would yeild well.
And be even more so if user accounts are verified to be unique (no Sybil attacks) so each signed viewing would be guaranteed to be a unique human. Currently Steem can't guarantee that, as anyone can sign up multiple accounts.