Getting hextech annie will cost you over $300
So I decided to get 15000 rp and bought 25 chests every day to see if I would get hextech annie.
I didnt even get halfway.
For every 25 (daily limit), I only got one gemstone. That means for $100, I only got 4 gemstones.
If you're looking to get hextech annie, you'll be looking to spend $250-350 (sometimes the 25 chests didn't have any gemstones at all)
In my opinion, not even the random skin makes up for this fact unless you have a lot of skins you can just disenchant for other newer skins.
So TL;DR - be prepared to spend LOTS of money for this skin. IMO $100 should have been enough. This is ridiculous riot.