[strat61caster]

Personally to me, aftermarket parts decrease value on most cars because I don't think I would want the same exact things as the seller, it will be added hassle for me to get the car the way I want it.

That aside, if I decided I was going to put the same parts on, this is the car I would make anyway and I plan on buying the components if the car doesn't have them already, I would not pay real value of the car plus new value of the components, those components are used and as far as I know used hard and possibly installed poorly/incorrectly, I would expect used prices on the components.

$21k car with $6k worth of parts into it (assuming that's $6k for the parts new) I would say $24-25k is fair depending on condition and how much the buyer wants it.

If you're already devaluing the parts in your OP down to $6k from say >$8k you might be able to find a buyer for the whole $27k, but idk what that stuff is worth.

Oh and does this include the original parts? If not then knock some more off the pricetag, that $21k is for an OEM car, why would I pay $21k for an OEM car without OEM wheels, intake, head unit, etc. Some people don't value that stuff, others do.