Sublime Starlight Challenge is too expensive

The description says use the following runes in runesmith craft but the cheapest recipe to use mountain rune + power rune is 25 divines. This is outrageously expensive for a trashy challenge, I think these craft recipes were poorly thought and challenge condition should be changed down to 5/10 instead of 10/10.

https://www.pathofexile.com/forum/view-thread/3548450
Oh, I wasn't aware there was already a discussion about this in another forum section. I'm facing the same issue and have no clue how to tackle it.

So far, I've found zero high-level runes on my own. Upgrading lower-level runes is practically impossible—it would take months of hardcore gameplay. Purchasing them isn't a viable option either, as the cost runs into hundreds of divines and is likely to increase even further.

I could do many, MANY endgame grinds before completing this one..