I would think it would fall around $2-3000 assuming there is interior finishing work to do also.

What is a normal exterior wall? Where I live that would be concrete. You need to get quote from a local contractor .I would think 2500 for labour is pretty steep but I honestly have no idea of pricing in Georgia,

The exterior wall I have is wood/drywall on the interior side, and hardiboard siding on the exterior. Not a concrete wall.

Still the same answer you need local pricing.

The approximate cost that Labra Design Build gave you sounds about right but I would budget for a bit more just to be safe, you will need drawing detail for the permit, permit costs, etc

Your best bet what PPF suggested is to get a few local bids and compare apples to apples.

Price also depends on how you want the exterior of the excavation finished. Wood timbers? Vertical metal? Terraced effect step?