I think the price is just a marker of how undesirable these big fuel guzzling high road tax cars are nowadays. I thought about a new, small congestion free car for the wife and out of interest asked for a part ex value for my omega sport. 2003/53, 25K miles and mint with no rust at all, fully serviced and brand new tyres. 3 different dealerships for 3 different makes all offered me approx £800 as trade in.
In comparision your car in elite spec is valued by glass as below for a part ex:
Estimated value of your car
Part-exchange Price:
Excellent condition: £140
Average condition: £120
Below average condition: £90
Please note: Unfortunately, we don't have a valuation for the requested mileage. However, we can value this car at 150,000 miles.
So for something that has done 205K miles + rust, they are not way off. Im not saying that you cant sell for more privately, but they are a buisness and what you could get extra privately is their profit margin. The other thing is that these sort of websites are better for more desirable and higher value cars. On a car worth less than 1k, take away a margin of £500 (I was told that is what they operate on) and you have a car that is not worth a lot to sell to WBAC.