I had never heard of Gemcraft till reading your comment, so I just looked it up. It's surprising to see my concept has basically already been made. I even had the idea of creating a gem-merging mechanic.
As for the gems being cheaper, I totally agree. I think I shouldn't have aimed to make the game "endless" and instead had a target wave to beat. I knew I needed to make the game scale in difficulty so the game eventually ended, but I definitely made it far too hard in the earlier stages. I'm planning to make some balancing adjustments after voting ends. I've also considered adding a "sandbox" mode of some kind that gives you infinite money.