So ESPN's free agent tracker which lists what they think every play is and what a starting salary for a multi-year contract would look like.
They have Wes Matthews as a key reserve with a projected salary in the 2-4 million range. Key Reserve is behind rotation, so that is like a 10th man type slotting.
They also do list Drummond as a starter in the 10-12 range (so slightly more than the full MLE).
Some other players with Boston connections or possible interest: Ball 18-20 million, Fournier 14-16 million, John Collins 24-26 million, Theis 8-10 million