The amount it takes to earn a top tier champion like Batman and Superman is around 48 hours and the first 20 levels. Whatever xp merit bonus week they gave us, it wasn't a bonus at all.
But the amps are fair considering once you unlock them, you have them forever. And really you only can make 3 sets of amps. So you only have to buy 9 amps which would be around the cost of 9000-1100 merit.