most sell for 70k minimum. But buying is not the only way to get a sigil, you can win them in HoH.
Oh and to get more money you can have each person in the guild give you like 2k and you should have enough depending on how many people are in your guild. Just because you are the leader does not mean that you have to pay for all of it.
Buying Sigil.
phearless
dansamy
As the leader, I made the majority of the 65k we used to buy ours. I think donations from other members came in the range of 10k.