And I really have to get the rest of them on my 
site soon!  >_<

One of the modifiers for price is the particular 
scene.  If the centered head shot of Yue that you 
are talking about is from his beautifully 
poignant conversation with Eriol and the last 
time we see Yue in the series, it could be worth 
up to $1000 (!) to some collectors.

Centered shots of Yue from the Final Judgement 
episode or the episode that centers on a change 
in his relationship with Touya could also be 
rather pricey.

I have seen cels of Yue (especially from the 
Final Judgement and THAT episode with Touya) go 
approximately this high in yen on YJ.

If instead, it is a nice but not wildly 
significant shot of Yue, $100 - $250 might be 
more reasonable, depending upon what the 
collector paid.  Again, this is judging by the 
prices Yue cels fetch on eBay and from the main 
sellers' websites.

Good luck!  And if you get the cel...please post 
so we can look at him in your gallery!

^_^