When I was doing research on
ECU's, I too thought that there was a huge price difference between the Autronic and the Motec. However because of the plug and play Motecs, the price difference is not really all that much (in the grand scheme of modifying a car anyway). My advice is to do as much research as possible into all the alternatives and more importantly, work out what you want to do with the car, both for now and the future.
Darren