very difficult to answer without seeing the vehicle,but just bear in mind in the bodyshop world to do it properly it would require painting the whole panel ! not just touch in or part paint.
The other option is the 'smart repair guys' like chips away but they very rarely get a 100 % back to factory finish, depends how good the guy is.
If you want it back to "it's former glory", I wouldn't try doing it yourself. I agree that the best path would be get some quotes from "smart repair" people...but it won't be cheap, even then.
Jenny, depending if the scratch has gone right through to the metal, if thats the case a Body Shop, if not, there is a product called,
"FARECLA" G3 Regular Grade compound, this pasted is used to cut the Original paint back to it's glory, it can be bought off ebay, you may only need a tube to try, but as said, if its down to the metal, a body shop, do not go to the dealers find a local family run garage and get a few quotes.
believe it or not labour rates in bodyshops are not as bad as you think, its the paint that can be expensive...theres one particular colour that we use thats £800+ per litre