Keeping it on the FREE side of things...
What I've been experimenting with is creating parts with MT, then substituting individual notes with samples gathered from around the internet. This isn't accomplished within MT, I put the substitutions on a separate track - drag and drop the files onto the separate track as separate items. Just align them with the notes in MT they're replacing.. or stacking to. It's tedious and time consuming, though.
I believe you can add other drum kit plugins in your DAW, then route their samples back through MT to accomplish much the same. Haven't done this but instructions are available.