fisheyes is indeed correct, there are many, many just starting threads & even just few about maximising what you can squeeze into a Purge Coterie.
Just hit either the Army Lists or Tactica threads & you can't go wrong.
Without going into the why:
Cookie Cutter 750
Lhamean, Cannon Venom
2 x 5 Warriors, Incl Syb, HWG, Cannon Venoms (WL)
3 x Reavers, CC
5 x Scourges, 4 x HWB
2 x Triple Lance Ravagers
Very standard, easy to adapt to 500, easy to expand & not THAT expensive $ wise.