The majority of blue spinel has a significant grey mask and hence lacks the blue hue of a fine sapphire. This, combined with the fact that spinel is significantly less popular than sapphire, results in a lower overall price. However, the benefits of spinel are its rarity of treatment (it is occasionally heated or fracture filled), and its exceptional luster, fire, and durability. It has a high refractive index. Due to these factors, some people ignore the greyer colour, particularly in a well-cut spinel.
Additionally, they lack the zoning that sapphires exhibit. This has resulted in extremely high prices for unheated sapphires - especially since the emergence of the Kate/Diana ring.