It is, but you have to admit, below 20 Mana - there's still no real Use-Case for it. If you play snipe, you will be low on health and also need decent speed. So you'll end up spending 10-13Mana for this summoner and speed. That is a lot!
Basically the area where these new Legendary Summoners are operating is really in the 30% high Mana Games... and since the supply is also very low, I guess we will not see him below Champion anyway.
But you are right, I'd say the price will be around 10$ a piece.