Say $200,000 for a reasonable elderly 727, $50,000 to mod the back of the aeroplane and get an STC $3000/hr in running costs including the crew. Let's say 10 punters per go, one 2hr trips per day, working Monday to Friday.
If they can really get away with $3000/ride, they'll be in profit by the end of the second week, and making $½m/mth thereafter.
Damn, why didn't I think of it first.
However, you seem to be correct, a quick websearch shows
http://www.nogravity.com/ and
http://www.amerijet.com/news/news31.html
(I'm sure by the way that my guesstimate is miles out - the operating costs will be rather greater including training / briefing, etc, but on the other hand the website says they'll take up to 27 people at a time. As JT says, a nice little earner.)
G