Try minnowbooster , they have a moving profit calculator. They try to at least give you a 120% profitability ( although steem price increase or decrease is a factor. )
For example you send $1 SBD , minnowbooster should upvote you at least 120% worth of that in SBD and STEEM rewards.
Have a look at my profile as an example. I've mainly used them compared to other competitors due to the profitability.