The easiest solution is simple say they're artscale. That also allows you to model details onto them with a bit more creative freedom, especially considering they're Chaos. Also, remember GW seem to be pushing for larger infantry models to be on 32mm bases, so it may not look too out of place.
For only ten models, £35 seems increadibly steep for cultists. You could get near twice as many Slaanesh marines for that much. However, I can see how the look works, and it would certainly add some variety to the cultists that are played.