If you plan correctly and leave some talisman at level 39 and 49 then it doesnt cost much to complete the leveling missions. The big cost is evolving 15 4* talisman at 1mm gold and 135 3* evo runes. The 1mm gold is recouped from claiming the cosmic talisman with the gold idol as a bonus. Since you have 15 days to complete this event it cost less than 100k gold a day. Completing all missions earns you 150 ironite which offsets the gold expenditure so this event is gold neutral.