Car starting problems again - Suspected ECU failure

1996 P reg Fiesta LX 60,000 miles.

First a bit of history. Last winter I had a lot of problems with the engine starting. Every now and then I would get in my car in the morning to go to work and then find that it did not start. Prior to that I had stalling problems at junctions as I went to stop. No one ever worked out what the reason for these problems were. First my car's version of the carburettor (apparently it doesn't have one) was supposedly dirty. That was cleaned up and filters changed. Next the car was re-wired, I can't remember exactly but the wiring was supposedly corroded. Then I had a mobile mechanic change the spark plugs and he snipped the end off one of the hoses which had a split. The final time which was in March I noticed there was creamy gunk in the oil, that apparently was just condensation. Let it sit a couple of days and it started again.

I had no problems what so ever during the summer until yesterday. After the cold and snow event of yesterday morning I decided OK let's check that my car is OK seeing as I had protected it with a cover this time to try and prevent the damp getting in (I shoved it in the bonnet though as it's too big for my car and the wind blowing it about would have drove the neighbours crazy). It didn't survive. The car is refusing to start. I had a mobile mechanic round today who couldn't get it going but did some tests saying he has a feeling that it could be a problem with the ECU and has been all the time. He couldn't find any problems mechanically and said he ran some tests which is why he suspected this but being a mobile mechanic he couldn't fix and said it needs taking down to a garage to be plugged in to have the electrics and ECU checked over.

So I found a auto electrics place who kindly said they will come pick my car up for me tomorrow. I thought it's best getting them to look rather than my normal garage as they specialise in electrics.

So the question is if the ECU has failed is it worth getting it sorted? Is it a big job? Expensive?

EDIT 25/11/2008: Appears to have just been damp and cold again taking 2 days to dry out like last time. Garage came to pick it up, tried starting it and it started. Any tips for keeping it dry as plastic in the bonnet didn't work? I don't have a garage.