Add more meta to image field

I have form with an IMAGE post field, and I have "title" and "description" checked off under the meta information. I'd also like to add two additional fields for each image post field -- medium and price. My form has multiple image fields, so I don't want to have a separate field for each of these values, but would rather attach/group them with the image meta. Can you point me to where I can customize the meta options available for post images? Thanks

Thanks Chris, actually, we're not using the form to create a post -- we only used the post image field because a) it had the title/description/caption fields (which we also needed) and we wanted it to auto-create the thumbnails. So we don't actually need the data in the addl fields to be attached to the image field at the end of the process - just trying to get it to show up there upon data entry. But if there isn't an easy way to add more meta fields, maybe i can just add additional medium/price fields under each image entry. thx!