How much does a rune page cost?

I'm curious about the cost of a rune page. Could you please tell me how much it typically costs? Is the price fixed or does it vary based on certain factors? Also, where can I purchase a rune page? Is it available through official channels or are there alternative ways to acquire it? I'm interested in understanding the economics behind rune pages and how they fit into the overall gaming economy. Your insights would be greatly appreciated.