The cheapest way if you’re absolutely in love with the car is to sell it and get a 2003 Lancer Evolution. They look very similar, but under the hood they’re entirely different cars. You’re driving an economy sedan with some sporty-looking bits bolted on for visual effect. The EVO is essentially a street legal rally car. This is still going to cost you a lot of money, but not nearly as much as making your car fast would cost.
Making your car fast is going to involve a whole lot of modification. Start with the brakes - Porterfield R4S pads all around and high temp brake fluid. Then the suspension for better handling. Larger wheels with lower-profile tires to match.
Now you need to put in a better clutch so that it can take the power of the engine. So far you’re into this for somewhere around 4 or 5 grand (parts only) and you haven’t added one horsepower. Let’s change that:
Garrett T25 turbo kits can be had for your engine. Everything you need will clock in at about $2,700. At 6 pounds of boost (don’t go higher or you risk wrecking your engine unless you build up the internals) you can expect around 50% more horsepower.
But now you’ve spent almost 8 thousand dollars and you’re not even done – you’re still going to need to do some fuel system modifications, probably need a bigger radiator, and eventually you’re going to realize that 6 pounds of boost, well, sucks and then you’re going to want to harden your engine so it can take more at which point you could probably afford a decent used Porsche Boxster.
You could sell your car for between 2 and 5 thousand, depending on condition. Let’s be pessimistic and assume 2.
Ten thousand dollars will buy a lot of cars that are a lot faster than what you’re driving now. Gimme 10 grand and I’d be able to come home with a V6-swapped MR2 that would wipe the floor with a turbo OZ Rally, and I’d have lots left over.
If I wanted something bigger I could get a 2005-2006 Acura TL with 100 more hp than the turbo-swapped OZ Rally. And, yes, if you look hard enough you can probably find an EVO for 10 grand, although I wouldn’t place too many bets on how ragged out it would be.
What I’m driving at here is that your car looks neat, but it’s just not economical to try and make it something it’s not. You’d be much better off selling it and buying something else.