Your Fiesta takes 6x9s in the rear and 5x7 in front doors in stock form. You have plenty of options for the rear 6x9s. Look at JBLs in this range. They can handle a lot of power and you can also run them in the RBE(rear bass enhanced) mode to act as subwoofers. Look at the beastly JBL 950si. Once you amplify them, you shall not need a sub.
For front, you can use an adapter to fit up to a 6.5 inch round driver- I suggest you look at components for front. If budget remains a constraint, a good 6.5 inch 2 way is an option.
Good luck!