It sounds like you are combining Alchemy with Runes to mimic (lack of a better word) other forms of magecraft. I like this. How about you use special ink to write the Runes? Like anything related to fire you use ink infused with ashes, or ink with sea salt for water. Could help cover the equivalent exchange, also infusing the ink with your own blood could add an extra kick. Or the blood of others. Or part of your servant, now there is something, especially if they are from the Age of Gods.