I got a follow up email from one of the cabinet guys I talked to. He ended up asking around and came back to say I am crazy if I don't get my builder to do it at that price
And I was able to talk my builder down
I also just ordered 2 pieces of 12"x12" 1/2" tempered glass. 3/4" would have taken 3+ weeks and cost like $350-400. He felt confident the 1/2" tempered will be plenty strong.