Just look at Milton Robson's collection sales in a soft market in 2010 such as this 1969 Chebby Camaro that was one of 69 built that sold for $418,000:
http://www.rmauctions.com/lots/lot.cfm?lot_id=567667
And his 1 of 17 Ram Air IV convertible Firebird sold for $286,000 with commissions.
Then his 1 of 5 Ram Air IV Convertible 4 speed Judge sold for $682,000 with commissions.
....and we all recall this crappy fake prototype (*look at the rivets!- doh!) for sale at $200K+ or so:
https://www.facebook.com/pontiactestcartransamprototype
Ok kidding there.
But seriously the closest comp would be a 1969 Trans Am Convertible. I recall one recently at auction that hit $1.1M and didn't sell - as it was valued at $1.3M a few years back.
But 1 of just 2 Prototype Trans Am in absolutely perfect newly restored condition?!?!
I will say being no reserve, it sells for $861,000 without commission. But honestly topping a million wouldn't surprise me. Totally worth that.
Find another - right?