What happens when you connect the jump leads to the wrong terminals?

I have a Vauxhall Corsa T reg 1.0 car. Battery died whilst I was out last night and my mate tried to jump start my car. It was dark and we thought the terminals were black and red. Turns out they were brown and black and I was meant to attach the red jump lead to the black terminal and the black to the brown terminal. We did red to brown and black to black. The car didnt start and started sparking and something burnt and now no lights on the dashboard will turn on. My friend had a look and said i will have either blown the 60 or 80 fuse and I have burnt out the alternator and need a new battery. And this should only cost about £100 to fix. But worst case scenario I could have broken the ECU as well. Which will be about £800 to fix. So thats £900 total. And the car only cost me £1100 2 months ago. If its the £100 then ill fix it. But if its the £900 do you reckon it will be worth fixing it or just scrap it and going for a new car? Because £900 is a lot to fork out on a car that only cost £1100.
And does anyone have any tips on how to fix the ECU at a cheaper cost?
I've tried to explain as good as I can, but if theres any more info you need to help me, just ask.
Thanks in advance!