I am looking to buy a 15" Macbook Pro but I only have a limited budget so looking into getting a 2nd hand one. As this will have to last me a while I'm wondering which model/spec I should look out for. I do web development and graphic design so can't get anything smaller than 15" screen. What can I reasonably expect for £500ish? I don't really want to go down the PC Laptop route if I can help it.