Different subsets of a selection custom field
To do this via webform_civicrm

Download and enable webform_civicrm and read the documentation. 

Google for some answers on SE or our blog at fuzion.co.nz/blog for some explanations about doing Events via webform_civicrm eg

https://www.fuzion.co.nz/blogs/registering-multiple-people-multiple-events

https://civicrm.stackexchange.com/questions/tagged/webform-civicrm

How can I create early bird fees with Webform CiviCRM?

Calculated member fees