I've read your disclaimer, and sorry if l am wading into dangerous waters when l bring up cultists here...
Though if it's the aesthetic level that you feel strongly about might l suggest looking at ANVIL Industries line of infantry models?
Cultists can undeniably be very cheap troop slots fillers for detachments, leaving you more points for more killy Chosens and what not.
ANVIL Industries are in quite some competition with Forge World when it comes to infantry models. Noticeably cheaper squad bundles, none of the bad dealings with Resins parts,
and the main reason: PHENOMENAL VISUAL CUSTOMISATION!
Arms, legs, torso, pants, heads, and actual heavy weapons options are all available and most are included in the base price.
A ten men squad from them is 2/3 of the price of 2 boxes of 5 scions from GW (brand new and not on Ebay though).
Now sadly no matter how much cooler they look, they still have cultist stats, but the parts from ANVIL industries can make any human look you want.
Price is might be the deal breaker, but here it's quality (and definitely variety) over quantity.
A long way of saying there are models out there of wargaming tabletop quality that can make awesome and unique looking cultists/scions, just didn't want you to the feel that GW is the only option.
The list looks solid for ranged and melee, though if a common opponent for you is Tau... then several deep striking crisis battlesuits could be problematic without sufficient bodies to screen your damage dealers
Happy army building