Why does a garage have to do it?
They're both really simple jobs, ECU is just unplug and plug in another. Whatever year your car is, get hold of a pre 1996 one for your car. OBDII have the ECU and the key coded. If you got a post 96 ECU you will need new clocks, keys, ignition barrel and all the locks. Pre 1996 weren't coded so it's a straight swap