probly could take the long way and give a specific bounty to each unit type through triggers, something like unit is killed, type of unit being killed is equal to (your unit here), add 50 gold to killing units owner
bountys Events Unit - A unit Dies Conditions (Unit-type of (Triggering unit)) Equal to Footman Actions Player - Add 1000 to (Owner of (Killing unit)) Current gold
but i suggest that you may use the point value as bounty,this would be easier to change the bounty :
bountys Events Unit - A unit Dies Conditions (Unit-type of (Triggering unit)) Equal to Footman Actions Player - Add (Point-value of (Dying unit)) to (Owner of (Killing unit)) Current gold
If you want to display the amount of bounty,you may use floating text triggers
sorry i jsut reread the question and its a bit misleading, what i need is if a certain unit makes a kill i want the bounty for the unit to be half what it would be for any other unit. Eg a super hard boss makes a kill and only gets 1/2 bounty but if a normal footman makes the same kill he gets 100% bounty