It doesn't make any sense to me that it would cost $35K "to open the safe." If all you want is basically a pro-rated value, you could use the IGS value charts yourself, or you could buy a copy of the Drucker publication, "The Guide." or you could buy a $30 subscription to gemval.com, which has graphed gem prices by species since about 2005. It is basically a look up task. Your potential buyer could do the same. The problem I see is that you are asking someone to come see a stone with very little assurance that it actually is worth what you say it is worth. You Gem ID report doesn't look like it is from a premium lab, so there are questions before you start. A person or corporation with $13M+ to buy a large sapphire is not going to want to get on a plane to come see a stone which may be a complete bust. So I stand by what I said about needing a new appraisal from GIA or someone else who qualifies as a supreme authority.
I think you may know that phrase "you have to spend money to make money." That is probably the case here. If the stone is truly worth millions, then $35K to open the safe and a few thousand to have a good appraisal is just the cost of doing business and is less than a 5% commission. I would ask around for someone who acts as an agent to sell this type of stone and see what they advise.Try some of the big names in jewlery and see what they say.
I'm a bit worried about the I2 designation, as that doesn't tell me what areas are clean and what are included. Without knowing that, I can't credit the report or the valuation much.