Can I ask for cost to run a workshop in the follow–up period of my fellowship?

Yes, but you need to justify those costs.  AREF is willing to support the travel and accommodation / subsistence costs of external trainers and – if required – for external participants.  However, AREF expects your employing institution to provide the workshop location for free (no hire charges). AREF also does not support a per diem for workshop participants, except where it can be justified that the per diem provides only for food and accommodation: payments to motivate attendance are not supported by AREF.