Well, I can tell you i've seen regular cels of 
Van go from about $50-$300 depending on how nice 
it is.  Cels of him with wings, however I do 
believe go near or over the 1k mark, though I 
never actually tried to get one myself becaue 
it's just too high for me to even consider.

Kenshin OVA cels seem pretty rare and expensive 
to.  I havent seen a whole lot of them for sale 
yet and I do believe they are in the $100 for 
nice ones.