Engine.
Without having to tear into it, I have bought, MSD Cap & Rotor, MSD Ignition Coil, and Red STI wires all from the Fiero Store just so that it all matches up red with the engine, it really does make it look a lot better. Also a CRX Cold Air Intake, also just makes it look better, but that's just my opinion. All this less than $200
Bit dirty but heres a pic.

Interior.
Buy some nice seat covers, or look around for some nice seats that you can put in. Also, I have redone my whole interior black with Krylon Vinyl and Fabric spray paint. But theirs many colors if you like another color. This really changed the look of the inside, looks way better!
I also did the Cavalier Digital Dash, looks really cool! I would say for all in interior was around $200.
Don't have pics of the blacked out interior but heres one of the digital dash.

Exterior.
I found some nice 17" Enkei (DM5) rims on craigslist, $225. Just look around.
Front spoiler, (Skitime) that you can make from a spare front aero bumper, I bought one for $30 and added some driving lights $20 just like how he has them. If you buy some plasti dip you can also change the look of your car as you like, for example I have notchback and I blacked out the roof, and plasti dip the rims black, and front mouth lol and it really changed the way the car looked!
Suspension.
Poly kit, was $100 and that's as much as you need to spend if you do it yourself.
Kyb shocks and struts, around $150.
Lowering.
Cut the front springs, (I cut 2 coils off mine, to lower (free), and don't forget to raise your front bump stop. Might have to pay a friend a few bucks to reweld or if you can weld your self well then it will be free.
DIY coil overs, also around $150-160, this is for the springs and sleeves. can lower or keep stock height but why when they look better lowered right.
Just take your pick on what you want to buy first, and on your next $200 just buy the rest to finish it all up, so if you can only spend $200 at a time, just buy the parts in sets, like how I have listed and when you have them all, just install all at once (I mean this for the suspension). If you do all the work your self, it shouldn't be more then what I have listed, I did all the work myself.
Heres pics of front with added spoiler with driving lights, I know the paint is messed up, the black is plasti dip.

Here is a side shot of the car, showing the plasti dip roof, also the rims, that got plasti dip cus they were gray but I thought they would look better black. and you can see how its lowered.

Hope that helps you some!