With concrete, gravel, re-bar/wire mesh, forming lumber and delivery costs plus labor and removal of excavated soil, it might not be a bargain price but I wouldn't say it's insanely overpriced as a stand-alone job. If it's being done at the same time as the driveway or garage floor, I'd say there's cause to object.
JMHO

randy427, thanks for your reply. I asked around and normally the price should be between $5 and $10 per sqft. So I think the sales guy is asking too much for a 4x4 concrete slab, especially when they can pour the slab when they build the driveway.

Just for fun, consider that a slab that size 4" thick will weigh about 800 pounds, without steel. $1.00 per pound for concrete sounds expensive.

I got prices from $5 - $6'/sf ft to pour/finish a garage slab.
I just formed and poured/finished a 3' x 3' slab for a new AC condenser. Small slabs are easy to do.
Can't imagine, someone who does that kind of work would spend more than 2-3 hours for the whole job. Closer to 2.
Dig hole and form.-1/2 hour?
Mix redi mix and pour/finish.-3/4 hour?
Clean up 1/4 hour?