I know pornography has existed pretty much since Greek civilization or maybe even earlier, and hookers too. However, pornography was either something completely outlawed or a thing only the incredibly wealthy could get their hands on if they wanted to. Where and when did pornography (and to an extent prostitution) become something a working citizen could purchase instead of just the rich. And I guess as a follow up question, what kind of citizen would be the first to produce porn, seeing as most of them were either in factories/mines or the artists/students had no time for that kind of stuff (probably).
Quite famously, the brothel in Pompeii was preserved by the eruption of Vesuvius where there are several (NSFW) frescoes depicting services or perhaps were just erotically charged art for the place. Some pictures of this are available here at Atlas Obscura: http://www.atlasobscura.com/places/the-ancient-brothels-of-pompeii (again, NSFW)
Prices varied, of course, depending on the service requested, but apparently were affordable for the common person, as per Erotica Pompeiana: Love Inscriptions on the Walls of Pompeii (Varone, A.). Some examples:
Maritimus licks your vulva for 4 As
or
The house slave Logas, 8 As
"As" being a bronze coin of low value. See http://www.littletoncoin.com/webapp/wcs/stores/servlet/Display%7C10001%7C10001%7C-1%7C%7CLearnNav%7CGuide-to-Ancient-Roman-Coinage.html. For the cost of a few loaves of bread, you could have sex with a prostitute.
edit: Of course, this kind of availability may not be the norm for a time period you had in mind. This is the example that immediately leapt to mind for me, and I can imagine that there may have been similar instances of this prior to the Roman republic (Pompeii was preserved in 79 A.D. to give you an idea)