Exile is the removal of all benefits of that society.
I would think the region loyalty might affect that, so perhaps an exiled person would find max 30% of the taxes - but that would quickly shrink if their region has a new lord.
Historically exile meant leaving the lands, or going to some backwater place, thus removing any chance of receiving income.
But, the whole point is that exile comes from the ruler, so any benefits from being associated with the realm should be withdrawn. However, anything derived not from the realm but from their feudal position CAN'T possibly be withdrawn in any manner that makes sense.
Remove trading for the "in-realm only" trades, but allow them to still access all other market trades.
Remove their access to banks, because banks are realm focused.
Remove access to recruitment because recruitment is realm focused.
If they are a lord you can't remove the taxes from their region, because it is their region. You can deny their ability to cash the bonds.
If they are a duke, and retain loyal lords, the same applies.
