This farming is very time consuming especially on early level. You got a very few amount of coins after all. However it is gonna be faster to farm it the higher your raid level is. If you really want this stuff it might be wiser if you grind it ( for example in your free time today ) till you can't end it in one run, and then take it slowly till the end of event.
Dude I agree completely just get to level 79 on raid get already made +3 helmet. Buy rainbow sphere and shards. Then save everything for 20 days of 5 medium nrg potions!!!