A friend of mine has a Ford Focus and recently, the ECU was 'spiked' by a faulty HT coil pack (becoming a common problem apparently!)
The local Ford garage quoted just under £1000 to supply, fit and program a new ECU and also replace the faulty coil pack.
This seemed extortionate, so after a bit of searching on the web and phoning around, we found a place in Greenwich (Power Steering Services - Greenwich 020 8853 3343) they suggested that it would be cheaper to have the old one repaired than to buy a second hand one and have it reprogrammed to match the car.
I removed the dead ECU from the car and it was dropped in for repair.
It was picked up about 4-5 days later and I reinstalled it. the HT coil pack was also replaced and bingo, started first time!
Overall cost was about £250, a lot cheaper than Ford quoted!
Kind of makes you wonder if this is all Ford would have done?