I've got an Autronic SMC in my Cortina. Great computer - The software is easy to use and it can make a car factory smooth if tuned right (depending on cams e.t.c.). I would definately recommend it to anyone. An Autronic SMC installed and basically tuned would be around the 3K mark. Definately shop around and ask people who's cars run well where they were tuned.
You should also spend some time playing with the cold start and low end maps yourself, because it takes a lot of time and tuners don't work for free.
All the best mate.