This gives the artists nothing to go on. Usually you go to a graphic service and find a artist style you like and then say what you're looking for in a signature. Such as Pikachu, you could say what you want for colors, font etc. Then you say what you're willing to spend OR you read what they have posted on their service for their normal signatures. A lot are 500-750 but go higher the more you want, pop out/animation etc.