I purchased my own stone and it was a natural stone veneer and my cost for it was about $10.00 a sf...the cost to install it was $15.00 a sf....they would have laid Eldorado for $10.00 a sf and I could have purchased it for about $6.00 a sf. This application was for exterior and the masons used a vapor barrier and mesh along with the scratch coat.
To answer your question...In my area $55.00 is outrageous unless there is some hidden prep you are not mentioning.

Does that include adding the brick ledge to the foundation and the extra flashing details? In other words, was the home designed for stone with those details from the beginning, or are all the construction details needing to be added?

I have no idea what the going rate is. But lets assume a nine foot tall exterior wall.

55 x 1 (foot of length) x 9 (foot of height) =$495 a linear foot.

So a house that is 25 x 40 or 1000 square feet has

25 + 25 + 40 + 40 = 130 linear feet as perimeter

130 x 495 = $64,350 for cladding a small house in stone.
Of course this doesn't subtract for doors and windows, but 25 x 40 is probably a good deal smaller than a typical footprint.

We were quoted 5.25 per sq foot retail price for eldorado stone in our area. While we haven't gotten a formal quote for cultured stone installation just yet, our contractor estimated based on past installations $20 per sq foot installed...so yeah that seems pretty darn high.

Correction. The $55 was basic countertops in granite. The Eldorado stone is $20/ft. installed.

Thanks again!