Question comes down to:
How much you have left over...
Mileage and Type of motor/trans in your contour.
How much experience you have working on cars...
Are you doing the work yourself?
Have access to garage and tools?
I you don't have garage or tools, first mod is tools! :laugh:
Second is make sure you've done some maintenance. Amount depends on mileage. If its above 70K probably a tranny flush. Other things that are no motor/trans basis are fuel filter, plugs, wires. Some thing you wont get until you have the Cel or search the forums is to clean the EGR passageways on your intake manifold. Search and you will find out what I mean.
Since I don't know what motor/trans you have...safest bet would probably be an intake. Really not a huge gain, but it gives more life to car. Cost ~60-100 with adaptor and filter.
After intake, exhaust would be fine. OEM SVT dual or Trubendz setup are easily done if you have garage. You may want to consider what exhaust you get by the amount of noise you want to put up with. :laugh: Loud exhaust + daily driver = UGH. Price if you do it in a garage 300-500 for trubendz. SVT exhaust depends on what you pay from someone with an SVT but probably around 150 if you pick up the exhaust in a truck.
After that probably wheels are tires unless the suspension is due. Getting off the 15s and onto SVT 16's or an After market set of 17's would make a difference in handling. You also need to put a decent tire on the rims, cheap does not mean quality. The 15's have alot of noticeable sidewall flex on a crappy set of tires. I would know. :laugh: This can run you anywhere from 350-1000 depending on condition of rims and tires (lower end being used rims with used tires).
Another consideration that easily done are the rear sway bar bushings and end links (pretty cheap @ ~40 bucks) At higher milage mine were worn out.
Realitively free is to debadge your trunk lid. Remove teh gay auto store license plate cover.
Cosmetically: Paint your oval grill, clear corner head lights, high tower head lights (search on these). There are audi side markers that can be swapped with your badges on your fenders. Swap your 98+ sail panels on the rear doors to plain pre98 panels (basically same thing w/o Contour on the panel). Pre-98 Antenna base (was chrome over black base). You can also paint the middle red reflector to match your car. Swap to a bullit aluminium gas door. Buy the "bright white" or "cool blue" headlights. Also install Fogs if you don't have them.
Other things include: Radio, speakers, dash warp repair kit, Contour.org logos

laugh: ) and window tint (which is generally illegal but alot of people do it). Underdrive pulleys if you find a set (~160-200 Duratec, ?zetec).
big step: Full suspension rebuild ~800-1000 bucks which would include struts, springs, ball joints, bushings, wheel alignment etc. Or Headers if you have a duratec Block (700 for all kit from MSDS, search). There are many Zetec heads, not sure which one(s) fit a Contour.
Advanced projects: SE into SVT via body SVT body parts (alot there were no "goldish tan" SVT's so all panels would need to painted) or a 3L swap (~3k)
So if you need anything else after that list to decide upon one of use may need to slap you with a rookie stick. :laugh:
If I forgot anything, let me know!