Time for few numbers (after discussion for mana hybrids in event thread):
Main Hall mana upgrade costs:
lv...Mana
22-133K
23-160K
24-192K
25-230K
26-280K
27-330K
28-390K
29-470K
30-550K
31-650K
32-770K
33-910K
34-750K
35-850K
36-1200K
37-1500K
38-1570K
39-1830K
By chapters (2 levels combined):
9-293K
10-422K (+44%)
11-610K (+45%)
12-860K (+41%)
13-1200K (+40%)
14-1680K (+40%)
15-1600K (-5%)
16-2700K (+69%)
17-3400K (+26%) (ch14-17: +100%)
Mana hybrids Production:
Burning Pool (4x3 12h) / Mana Sawmill(2x4 6h):
9 2700 / 720
10 3600 / 950 (+33,3% / +31,9%)
11 4700 / 1260 (+30,6% / +32,6%)
12 6200 / 1670 (+31,9% / +32,5%)
13 8300 / 2200 (+33,9% / +31,7%)
14 10900 / 2900 (+31,3% / +31,8%)
15 12600 / 3300 (+15,6% / +13,8%)
16 12900 / 3500 (+2,4% / +6,1%)
17 13300 / 3600 (+3,1% / +2,9%) (ch14-17: +22% / +24%)
Between ch9 and 14 both mana increase costs and production increases were prety stable, costs rising slightly faster than production.
In ch15 mana cost for Main Hall slightly dropped.
In ch16 & 17 mana costs for Main Hall rises much faster than mana production.
Even including ch15 with the drop price, the price rose between ch14 and 17 by 100% (doubled) while mana production rose only 22% for Burning Pools and 24% for Mana Sawmill.