Excellent observation. I didn't realize it until today but I am getting as many coins or almost as many in campaign as I am from spider. I have to run the numbers, but you're getting points for leveling champs and from the artifacts.
I agree with both Swiftblade and Angwil on this. At first I came into this event thinking it was like the last one, which was painfully expensive to get any reward, but after playing around with it the champion training aspect of this one actually makes it significantly easier to get some of the items.
I think I saw some math and videos floating around, but it essentially boiled down to about 4k energy to get the leggo book or 5 star chicken, which is a price I'll easily pay. It's even less if you use a bunch of XP Brews.
I have also essentially just built a bunch of food champions and walked away with simple rewards, so in that facet I actually quite liked this event. It is much better than the artifact enhancement + dungeon divers combination from before