A hundred dollars is a pricey cel. The one of Zasu would only be 25-30 dollars or so. There are a lot of factors that affect the price of a cel - physical condition, number of layers, layers stuck/unstuck, background included, dougas (pencil sketches) included. Besides the physical factors, there is also the artisitic content. Main characters (Hikaru, Umi, Fuu) will always bring higher prices than minor characters like Zasu, sorry. ^_^;; Facial close-ups also bring higher prices, a particular pose or pleasing facial expression can also make a cel worth more. Special scenes can bring high prices an example of this would be a wedding scene with a main character in a wedding dress. Because it would be both unusual and beautiful, it would look more attractive on the market.
For me, the first impression is everything. The first time I see the picture tells me if I want the cel in the first place. Then judging from past experience, I'll somehow figure out how much I would be willing to pay for it. Sometimes I get outbid, but that only means the cel was more valuable to someone else than it was to me.
Hikaru-chan's Magic Knight Rayearth Message Board