Ambient gold (simple) math
Just a quick look at the ambient gold changes that are being used to justify all item cost changes.
FOR DOING NOTHING, YOU GET 9.5 gold per 5 seconds ⇒ 10.2 gold per 5 seconds 9.5 gold / 5 seconds = 1.9 gold per second 10.2 gold / 5 seconds = 2.04 gold per second
2.04 - 1.9 = .14 gold per second increase with the buff.
.14 gold per second * 60 seconds = 8.4 gold per minute extra. 10 min = 84 gold 20 min = 168 gold 30 min = 252 gold
Wow.