My recommendations?
Do your research--you're already reading the rulebook, but that's only a guideline. Go to the track, check out varios websites, particularly those dealing with the kind of car you want to build (a Duster) and start getting opinions. Everyone's quick to voice their ideas, so that shouldn't be a problem.
Once you know what you want, at least consider buying a used car--they can be had for pennies on the dollar. What you don't like, you can delete or modify. Start off simple & gradually work up to the e.t. you want to run. Don't think you can jump into a car & instantly run 9 or 10 seconds--you'll only disappoint yourself.
It sounds like ultimately you want to run a moderately fast purpose-built car, so I'd consider perhaps a big-block powered car (less maintenience), normally aspirated (easier on parts), mini-tubbed ( less expensive to build) with an automatic trans (more consistent). Such a car, turn-key could be had for anywhere from about 8k on up depending on its mods, age & how complete it was.