The sample art would remain in possession of the artist unless the artist was contracted to do the entire project. It is merely to assess capability. I have updated the prompt for clarity--we did not mean for each sprite to be precisely 640x480. Rather, we want the art to be "at home" in that resolution, if that makes sense. An average character would be about 215x215 based on the reference images we were using from Street Fighter 3.
As you can probably tell, our grasp of the terminology is preliminary, so bear with us.
We used this article to obtain our pricing structure:
http://2dwillneverdie.com/blog/how-much-do-sprites-cost/We went with an average of the "high end" prices per sprite. (Article lists high end price for 500 sprites at 7000-20,000; 7k + 20k = 27k/2 = $13,500/500 = $27/sprite. We will gladly take some input from people as to whether or not that's a fair price, but from our offers that we have taken from some other potential candidates, we have determined this to be a fair, if not higher than usual, bounty. However, it's entirely possible that we are not conversant enough with the actual process of producing good quality sprites to know what will go into this, so if we need an education in this respect, have at it. We know the toy and illustration side, but the digital art is something new to us--we are only casually conversant in sprite art as gamers and fans.
We do not want to reveal any existing art at this time to protect the secrecy of the project.