ECU's don't usually fail like they did twenty years ago. Not meaning to challenge, but are you sure it's the ECU?

Try searching on a subject like "automobile ECU repair" or some variation of it.

 

Dear DS,

As you are in the UK, you have a few less options than US owners. However, you can still get a diagnostic run on your ECU at the Hyundai dealer. This is worth the expense to prevent you replacing a goo part. Get it checked, and let us know the results.

Byron

 

I just replaced my ECU. The dealer wanted over $1100 for the unit itself. I found a salvage part for $50. Try searching salvage yard web sites such as autopartsfair.com. It is fairly easy to replace the unit but you may want to have a mechanic put it in as it may need to be programmed. Be careful when purchasing because their are different ECUs for different models and production dates. I bought the wrong one at first but when I had the ECU out of the vehicle it was easier to locate the part with the model numbers.