Well, you can not create a custom field that is conditional upon another custon field. The fee fields you setup are only based on the user selection of that one field. In your unique situation, I would recommend actually creating multiple events for the one event. Then NOT using the front page list of DT Register. On your page about the event, manually create registration links for each user type (first time visitor, student, etc). Then on each of those \"events\", you can use the member discount function of DT Register along with any other custom field options you may need. Hope this is helpful. Thanks.