I also think it greatly depends on the scene.  
For instance, cels of Zechs and Noin from Gundam 
Wing can definitely get pricey, but I payed quite 
a bit for the cel below, although Noin's eyes are 
closed, and Zechs has on his mask.  But it really 
came down to the scene, in addition to the rarity 
of finding good cels of the two of them together.