How Much To Charge for iOS development

I am a fairly new iOS developer. I am also a sophomore in high school. Recently I interviewed for a job at a law firm. The task is to create a relatively simple application that will allow you to view laws and download them. It will also possibly offer access to newsletters and contact information. Not too difficult. But they have asked me too set the price. I have absolutely no idea how much to charge. I've tried to do research online but I haven't found a good baseline. Also I must keep in mind that they are hiring a high school student instead or a professional developer so I cannot charge them what a normal developer would charge. Could anyone tell me how much they think would be fair to both of us? Thank you!