I'm not sure exactly what you should pay, but you should realize that the chances the gecko will look like this in adulthood are very low. It's likely the gecko will yellow up considerably. If you're lucky, it will be a nice lemon yellow and not a yucky gray/yellow. I know this because I've produced a number of geckos that looked like this as juveniles and then looked completely different as adults. I would probably sell a gecko like this for $35-40 but I tend to be a bit on the low side.