How much is 1 ruby in Heroes of Mavia?

I'm curious, can you tell me how much one ruby is valued in the game Heroes of Mavia? I'm trying to gauge the worth of in-game currency for my gaming strategies and I'd appreciate your insight on this matter. I'm especially interested in understanding the exchange rates or if there's any fluctuation in the value of rubies over time. Additionally, do you have any recommendations on how to efficiently earn or acquire rubies in the game?