Simply randomizing the race on a sigil has extremely low value for its cost. Spending 3000 granite to pick a random race for a primal sigil when I’m looking for a specific race is not worth it. I’d be happy to spend, say, 30,000 granite to choose the race, however.
The randomization cost starts off at 1000 granite for Minor Sigils.
I do agree that we should be able to pay a high price say 50k granite to get a specific race.
That’s why I said 3000 for primal. 
Yeah, maybe we can spend 5000-10000 to choose the race of a minor sigil. That would be really helpful for, for exemple, get specific legendary materials.
What about if you could trade X number of sigils for one specific race of sigil.
Or that. Either one is fine with me.