It's not $5/bag. There's also tools to be bought or rented, knowledge and skills to learn, and time spent. $2k is the cheat code to skip all of that.
My calculus is to evaluate time, cost, and quality. If someone can match or beat me on 2/3 of those dimensions then I'll hire them.
He's getting downvoted, but he's not wrong - however, finding someone who specializes in doing this would be hard, and knowing how to word it so you can use "standard crews" would itself be $2-3k for a GC.
This is the danger of "cheap projects" - they can grow legs before you know it, and you end up paying half the cost of increasing the square footage of the house (or the garage).