He's looking good so far!  It's always hard to give feedback at this stage, because what your final goal is and what we're seeing now are not the same.  The things that are important at this stage are hard to see in a picture, so I'll ask some questions:  
 
Is he well balanced?  Stands solidly, not likely to tip over?  
 
Is the armature strong? Doesn't bend under the weight of the clay?  
 
What are your plans for the wings?  Will they be clay, Fantasy Film, ??
 
What medium are you working in? Polymer clay? Air dry clay?  (If it's polymer, be sure to bake according to the manufacturer's specifications.)  
 
Where are you planning to sell him?
 
Pricing is always tricky even for a finished piece.  Here's a decent article on pricing your work.  It's mostly about commissions, and she's talking about paintings, but many of the same principles apply:  
http://www.elfwood.com/farp/thebusiness/priceart/priceart.html
 

Cool!  It sounds like you've planned him out pretty well.  The only thing that worries me (and only slightly) is that you've mixed 2 brands of clay that have different baking temperatures, so you either have to overbake the Fimo or underbake the Sculpey.  If I had to pick one, I'd use the Fimo temp of 265, because overbaking is dangerous, health-wise.  Nasty fumes.  
 
You are using an oven thermometer, yes?  (I've never met an accurate oven.)  

Looks pretty good at this stage, I especially like the plates/ridges on the chest.  I think the back would look nicer if you arched it up a bit in the middle, kind of giving the body a snakelike flow to match the neck and tail, but it's up to you.
 
I guess the best advice I can give on pricing is what you think your work is worth tempered by what the market will bear--be realistic about the value, but don't sell it for a price that you'll later resent.  An artist I know once gave this opinion on determining what to charge:  "Pick a price, and then add a zero to the end."  I know you said you're going to a show to sell it, but if you ever do a more traditional commission, always make sure you get 50% of the asking price up-front, non-refundable (unless you fail to finish the piece)--not only does that cover the cost of your materials, but it usually culls out the people who aren't serious about purchasing your work and just want to jerk you around.

Quick Update
 
 
Ok so hes changed quite a bit since I last posted so I thought I'd post a new pic.  
 

 
I also added an arch to the back and everything, more pics comming soon!  

Thank you Eirewolf I've been working hard on him.  ^^  Here's a few pics of his body:  
 

 

 
I've recently starting working on the muscles and I think it's coming along nicely.  

I'm impressed with the progress you've made, the form has really improved.  The thigh musculature, and how it joins the body are superb.  The spines on the back have a bit of a Godzilla vibe to them that I like too.  I look forward to seeing how the final version turns out!