Most successful Oxford applicants have a high proportion of As and A*s. I think the average applicant has 6A*s, the average offer holder has 8. GCSEs are weighted more heavily than A Levels in some subjects. Only like 3% of offer holders for econ would have your GCSEs. Oxford look at GCSEs contextually, but that usually makes a smaller difference than people seem to assume it does.
Consider Cambridge and try and get A*A*A at A Level. Otherwise AAA+ should be enough to get you to a Russel group and into finance Other Unis care less about GCSEs too. If you got an average of 95% in your A Levels, Cambridge wouldn't care about your GCSEs at all. Don't forget about LSE, UCL, Durham and Bath. To be honest econ is such a safe choice employment wise any top 25 uni will get you a good job and in the right track
Also remember you dint needn't a econ degree for finance. Chancellor of the exchequer George Osborne has a history degree. A degree in maths, geography, neuropsychology, sciences etc. from a top 5 uni still lets you go to finance. Cambridge's land economy course has grads with the highest salaries in the uni, lots of management consultants and bankers. Have a look through all these courses and see what A Level subjects are expected/ wanted. Think about what you'd do best in, and take those to A Level and try your very best !! Top A Levels will really make up for those GCSEs ( which are still good by the way, but weak for top 5 Unis)
If you don't get predictions of A*A*A + then you apply after A2 in a gap year after achieving the grades.
Good luck, keep working hard, you can go into A Level and get amazing A Levels. With those, most Unis won't care at all about your GCSEs