Some numbers for you:
Given the 3.6% chance of a gem from a chest, the _expected_ number of trials (chests) to get 10 gemstones is
From event orbs which increase the chance by only half, there's a 5.4% chance resulting in an expected number of trials (orbs) at
(Both numbers rounded up to the nearest one because you can't buy a partial chest/orb)
Doing some conversions of chests to rp to to actual money, that comes out to:
If buying Masterwork chests. (Which I used because I own every champion, and like other veterans have no use for the BE from champ shards)
If buying only the 25 packs of orbs, which are only an option during Position Orb style events but are the option I used since they're currently available.
And that's only if you buy your RP in $100 increments.
Now, keep in mind that these are only the _expected_ amounts. Random chance can make it take less, but there's a higher probability that it will take more. In addition, these are the amounts for _one single_ Hextech skin. So nevermind trying to get more than one.
One aspect to note is that I did not factor in the 1/2500 chance of a hextech permanent dropping because it's so close to 0% that it doesn't really effect the odds. But I do want to note that the _natural_ chance for any particular skin shard **_should_** be 1/1030 since that's how many skins are in the game. They're artificially inflated past less than half the normal chance.
So I'm of the mind that expecting a $440 purchase for the chance to get a single skin isn't entirely fair, because we aren't even given the option to not gamble for it. If they could be purchased for $100 even despite all being less content than the $30 Ultimate skins, then the exclusivity may be worth the price. But as-is, attempting to get a Mythic skin is unfairly costly.
But barring that, I think lowering the requirement from 10 gemstones down to 5 (and the ward down to 3) would not only make it more fair to attempt to get one skin, but would actually help business as it would encourage some people who aren't willing to attempt to get 10 gemstones with such poor chances to go for gamble at 5.