One option is to build a form for the volunteers only. To do this you do not make the form public on your website but send the link via email only to those people who plan to volunteer. you could even start with a simple form to gather interest from possible volunteers. Once you get that first cut of potential volunteers you email them again with a second form that collects the money. they do not have to be assigned to any activity or you create a special volunteer sign up activity so that you can track them later prior to assigning them to the Kids Camp. In your volunteer forms you can ask specific questions you need answered so you know where to assign them later. you will have to manually connect these paid volunteers to the primary activity/job combination but at least you have a way to track them and their payment now.
Jeremy Jackson