If you don't have the money, don't even bother modding. Why? Not that your car will be unrealible with a few bolt ons, alot of people do mods and let good maintence go to hell. Then there car ends up falling apart. If you don't have to money to do both, and not let yourself go under (backrupt), don't bother.
If your truely don't have any money, save you money and keep your car maintenced and tuned up. You'd be better off. Now if you have a little money laying around, do a few small mods here and there, take your time. Do a major tune up first, then work on flow mods. Don't bother doing a pulley right away, thats where most people screw up and then they blow there motors. Don't even think about installing a pulley without a scanner of your own. With a good tune up and some flow mods your car should run a little quicker + even get better MPG and your car will be very realible. That kit your looking at on 3800 perf or where ever is NOT a good starter kit and you'll end up with mucho KR problems. You need a good flowing intake/exhaust, cooling, and PCM tweaks at least to be safe.
Once you start getting into bigger mods... pulleys, rockers, ICs, cams, heads, etc... You better make sure to have some money on the side. As the old saying goes, you gotta pay to play. When highly modifying ANY car **** is going to happen. Be ready for it, thats all I can say. I've been around the GP scene since 1999, around 9 years now and i've seen many come and go. Most people wouldn't have any problems if they would just use a little common sense, thats all it really takes to modify any car. Time, research, money, and common sense.
Good Luck...