10x Cultists = 50
Daemon Prince w/ Wings, Mark of Nurgle = 200
(or any mark of your preference),
You've got
AT (can Smash) with a mighty 2+ Jink (Shrouded, aww yeah). Also some Psychic Powers (don't quite know what Nurgle Princes roll on, but Biomancy would be good).
The
DP also gives you speed, due to being a
FMC so can easily get in your opponents face quickly.
Ofc, there might be other limitations (such as no
FMC/Flyers, models w/ 2_ save and so on)... but if it's campaign a Daemon Prince could be useful. Or a Heldrake..
EDIT: I did not see somewhat friendly...I'll revise this