$150-$250 Maybe $350 if he's a "proven breeder" but that's doubtful because of the age.

Depends what the seller wants, I wouldn't really pay more than that. I got my lemon pastel male for $100 as a baby.

The only way you would really know if it's a lemon pastel is if you know it's parents. It's a fantastic looking pastel if that's a picture of it at a year and a half.