By way of indication, my 56-plate (Jan 2007) 1.9 TiD auto Vector Anniversary saloon, in very good order with a full history, 6 months MoT, and 77,000 miles up, has been valued recently at £2200 - £2500 as a part-ex, £3150 if sold privately. The Parkers, Autotrader and What Car valuations all come out pretty much the same.
On that basis, a similar car at a year older is probably going to fetch maybe £500 less if the mileage is under 100,000. But if there's a lot more than 100k on the clock, or any damage, faults or missing history then you might be looking at £1200 trade-in, and perhaps £1800 to £1900 sold privately.
I must admit I'm a little surprised - I reckon that Saab 93 values are falling a bit faster than say equivalent Volvo S60 prices.
As for where to advertise, I guess Autotrader would be the first port of call, or Gumtree, or Ebay, or possibly the Carandclassic web site.
Plus of course, there's always the Classifieds on here!
I would think Saab residuals have been affected by the business closing. On the upside, I got a really good deal on my 11 plate SC three years ago precisely because of that, so can't expect it to hang on to too much value.