I think the idea is pretty alright. 
As far as I know the lowest price of gems are 10.
Something that I would change though, I’d prefer it if I payed for (example) a long and beautiful dress to have an impact in the story, just to be happy that I spend the gems, you know 
. But on the other hand if I wrote a story with gem choices I’d let the readers be happy with the choice they have made, but I wouldn’t make the person that didn’t click on the gem choice to have a bad impact. For example they’d just miss a beautiful dress or a bonus scene etc. 