I recon a good A4, with MOT and suchlike, thats been looked after would go for 800 minimum.
A 2.4 V6 FWD is certainly further down the desirability list than the turbo cars, but i'd expect that even just throwing it on ebay you'd see 6-700 for it without too much hassle, and probably a little more if its clean and tidy and in the right location.
What you need to remember, is the running costs and maintenance of a car should never be compared solely against its price, you need to look at the whole picture. For instance, your car may be worth £700, and some might say a £500 repair bill wouldnt be worth it. But on the other hand, if the cars otherwise sound, that 500quid is likely to fix a lot of parts and give it many years more life.
The alternative would be to sell the car for peanuts due to the fact that its broken and put the small amount you raised from selling together with the 500 the repairs might have cost, and buy another car, however theres no guarantee that new car wont also land you a big repair bill, as people do often sell cars when they develop faults.
I had the same dilemma with my old FWD avant. It was on 200k, and the engine was half dead. I could fix the engine, or bin the car, but when i thaught it thru, i realised that since i'd owned it, i'd replaced all the suspension, all the brakes, tyres were all good etc, but all of these parts were unlikely to make any odds when selling the car as "spares or repair" with a knackered engine... The only part left that could really go wrong was the engine, as everything else was new. So i spent nearly 800quid all told, fitting a replacement engine, along with a new clutch, timing belt, water pump etc etc. I knew it was a lot of money to spend on an "old" car, but even if i'd sold it as it was there was no way i could buy another A4 for 800quid that was as good as mine.
As it turned out, about two months later i found a quattro, and sold the car to my parents, but i know that the cars mechanically sound, and that they're going to get a decent life out of the car before it costs them big money.
