The main thing that keeps me from donating is the cost of stuff.

I can donate about $20/month and thats just enough to summon the runekeeper !ONCE! $20 wort of gems to get a blue gem and depending on my luck on legendary keeper (not even sure its 100% that i will get to him by paying the 200gems) probably get a blue or maybe a purple, odds to get a yellow of him are way to low to consider.

10gems seems a more reasonable cost to summon her, and even that might be a tad high depending on chanses to move on to final keeper.