Suzyann,
a couple of options you might want to try checkout who else in the family has a decent car that can be used, if they are prepared to let you borrow it arrange a nice valet the day before so its sparkling, that way you'll both be happy!
Check out a few hire car companies, see if you can rent a high spec merc/bmw, and then truss up a friend / relative into a suit to chauffeur you!
When if comes to your wedding, not just the car, see what discounts you can get.... develop a brass neck... I managed to get 20% off the wine, a better menu for the price of a cheaper menu, discount on a car....
It helped that I got married in january, but really ask every supplier for some sort of discount / additional service.
People won't remember the car / favours / chocolate fountain / bagpiper... but they do remember the wine with the meal!
Spend it where it matteres, its darn easy to flitter money when arranging a wedding!