Add-Ons to Events (with pricing options)

Can we have a Custom Field option as an "Add On" option for an event? For example, add on's for camp are an After Care option, swim lessons and diving lessons. These are an extra charge for all 3.  It would be SUPER amazing if registrants could simply add on one of the custom field options and simply get charged a little more than the normal price for the add-on. Having an event with extra options is always useful, add a shirt for an extra cost, little extras for an 'upgraded' experience to an event, or our needs (swim lessons, after care and a diving class option for summer camp). We also ran into an issue with this for guests. It would be good to have an option to 'add on' a guest with you to an event and the extra fee gets charged to the event price.