You are way off there.Second-run syndicated series do not generate the level of ad revenue you're thinking of. It appears most of the money is generated from the sale of the rights to a specific station to air the series: http://tvtropes.org/pmwiki/pmwiki.php/UsefulNotes/Syndication
There's also the case of "barter time," where stations sell ad space to the studio, rather than buy distribution rights to a less-than-popular series: http://filmescape.com/how-does-tv-syndication-really-work
Firstly, the $123,000 is a national average, because not every city charges the same rate. Secondly the price is charged on a Cost per Thousand basis. So if Deep Space 9 was airing on a station in Los Angeles, the rate would be higher than a station in Kansas City (about $18 per 30 seconds per 1000 vs. $7.50). So in LA, the cost to run in 30 second national ad (I.e Pepsi) would be about $17,000 (over $250,000 for seven minutes) if the station said you would reach about 500,000 people vs about $3,800 (over $53,000 for seven minutes)in Kansas City.
Plus there’s other factors to consider, such as time of year—-it’s more expensive in the September to December period because of Christmas. Also airing on cable channels (Syfy) offers higher ad rates than on broadcast channels (WXYZ ABC Detroit). Geographic location (airing in L.a. will cost more than airing in Watertown, New York).
Since TNG debuted Paramount and CBS have been using the barter system—-but they give the shows to the stations for free, and the retain the majority of the ad time to sell themselves to national companies like Pepsi, while the station has a small amount for local ads, unless they’ve worked out a network deal like Bell has for DS9 on SPACE here in Canada where the series is exclusive and Bell handles all the ad time.
Suffice it to say, DS9 in HD would be profitable for CBS.