The only way u could make it look decent and still make it subtract gold is if u did it in a trigger. Its not hard to figure out the trigger but if ur new it will take u about 2-4 minz to do it.
Ah come on, don't be lazy use triggers. lol the riflemen avatar looks funny.
Events: A Unit begins casting a spell Conditions: Spell = <Name Here> player has <certain amount of gold> Actions: Property Remove <gold number here> from pwner of casting unit.
It goes something like that. Anyways just try to work it out.