As for getting OEM parts, I'm assuming you would have to know someone to install them for you right? I don't know much about car parts or installing them nor do I know any good mechanics that would install them for cheap.
depends on what you want to install. for things like tail lights, grills, headlights, you could probably do yourself with some help from threads in this forum or on mazda6tech.com. for things like a lip spoiler to a wing spoiler, you'll need some help.
when you do buy and are looking for oem parts, check this site's sponsors who offer really good prices and customer service. good luck.
btw, i have an 04 5-door if you have any specific questions.