They charged me 4500 pesos when I went in for a consultation yesterday. Not that a 500 pesos gap is a big deal, but maybe you were charged extra for being a gringo?
Mind you, I had called them a few days ago and asked them in spanish about a quote for consultation, that's when they quoted me 4500 dop.
And just as in your case, the doctor recommended a battery of additional eye tests for an extra 12 000 pesos, but due to the high cost to benefit ratio I didn't bother (she said she diagnosed high intraocular pressure and so she wanted to test further for glaucoma, which I doubt I have seeing i'm only 33).