We went through the same decision a little while ago when renovating our house. We found that the fabrication cost component of the thinner granite made its total cost about even with the thicker granite.
You should talk w/your fabricator to get a true “apples to apples” comparison w/the Home Depot quote because Home Depot (I believe) includes both the labor and material, but you seem to be looking at only the material cost component when you consider the thinner granite.
You also should ask a fabricator the cost differences between the various built-up edges that you’ll need with the thinner granite (you can choose any type you prefer – ogee, bullnose, eased, etc – but costs vary slightly between them).
We found that the thinner granite actually looks slightly thicker when the fabricator built it up with the typical edge detail.
