I think stabs are probably the only “cheap” thing in foiling. Almost guaranteed to make a huge difference for a small cost.
I always have one HA and one MA, start with that combo.
HA for glide, MA for turns.
The difference between a bad and good tail is also amazing. If you can, get an AFS Silk tail or Takuma Kujira both are really good for MA, probably better than anything I’ve ridden for smooth push back through turns
They sell quite easily too, or chop the HA if it wasn’t too expensive once you start finding it too locked in for turns.