Sealed will require EQ, big or small...
Ported uses the tune of the port/cabinet to bring up the low end, but there's your tune, hope ya like it type of thing... though it's cheaper this way since PVC pipe costs less than a parametric eq unit.
Car boxes are designed for cars, which is a 20 cubic foot volume so yes they are small and lack the low end because 'cabin gain' at 9-10 dB almost offsets -12 dB rolloff of sealed boxes.
1. price out a good sub
2. model an enclosure for it
3. find whatever is closest to that enclosure, whether you had a cabinet shop make it, some car stereo place, you found a big wood box (lol, okay don't do that) or you decided to man up and try a little woodworking...
All other variants where you save a day of cutting or a few bucks for the moment will lead to mediocre results that you will probably grow to hate with time.
IMO save up and do it right, save up longer and buy something decent - something along those lines.