Rank 30 and 40 leves just shouldn't give any gil at all. Have them all give marks. Let new players get some gil from the lower leves still. Have all local leves give marks, but lower the amount each leve gives to compensate.
Whoever designed the economy in this game had no idea what they're doing. There's dozens of players per server now with over 100mil gil and that will take a long time to be removed from the economy.