paulaner wrote:

First estimate for the concrete job is nearly $8.5k.

Your slab will take something like 2.4 cubic yards of concrete (if it
really is going to be 4" thick).

The going rate for concrete is about $150 per cubic yard, maybe up to
$200 if you ask for pigment or fiber.

So the cost of the concrete shouldn't run you more than $450 to $500.

Your quote must be chock-full of preparation work, excavation, fill,
tamping, form setup, floating, etc.

The rebar will probably cost an extra few hundred bucks.

If you can do some, most or all the setup yourself (including buy and
set up the rebar yourself, forms, etc) then your price will come down
considerably.