Cels Forum

Hmm, getting Soujiro cels won't be easy.  There are way more Kenshin and Kaoru cels out there than of Soujiro.  Supply, the 2nd biggest factor in controlling prices of cels is working against you.  Of all the Kenshin characters, Soujiro was #2 in a fairly recent count.  Popularity would probably cause the demand to jump and demand is more of a price jacker than supply.  
Aoshi is also pretty popular but the supply is better.  Not by much tho...I had a chance to get 2 cels of Aoshi from the second OP, 1 close up of the eyes only and another chest up a little off to the side for $700 about a year ago. They're probably much more expensive now.
Kaoru may be a lot more resonable.  Shes in the entire series, so comparatively, there are *plenty* of cels of her. I've seen some D-class cels of her go for around $50 tho.  
I think Sony is still sitting on a pretty hefty stack of cels.  Geez....

If you ever ask yourself "why are cels from XYZ so expensive?" the answer is most often "because there are people who want it so much they'll pay that amount for it." Vega keeps getting Lodoss OVA Deedlit cels and charges a few thousand dollars each.  Still, they get snapped right up.