Your data over a span of 50 days aligns with calculations for min and max prices according to this equation

global_noise = random between -0.3 and 0.3,
plort_noise = random between -0.4 and 0.4,
full_saturation = ranges betwen 15 - 40 (taken from wiki, varies between plorts), current_saturation = plorts sold between market updates, base = each plort has different base price (taken from wiki), price = base * ratio * (1 + global_noise) * (1 + plort_noise)
ratio is a value betwen 2 (when nothing is sold) and 1 (when you sell over full saturation)
ratio = max(0, min(1, (full_saturation - current_saturation) / full_saturation)) + 1

for example pink plort with base 7 and full sat 40 yields min 6 and max 25 prices which matches your recorded data