Not trying to dog you, but you do get what you pay for with polishers. If you are spending much less than a Porter Cable 7424XP costs, it is probably not really worth buying. The 7424XP, believe it or not, is considered a great, inexpensive entry-level DA buffer.
If you don't want to spend that, IMO just do it by hand because cheapo ones won't have the power to do much more than smear wax on and make you feel like a detailer while using it. You need some power to do paint correction. The fact that the Harbor Freight one is $80 should tell you something because Harbor Freight is generally "disposal tools" quality.
If you do want to reconsider, search around, I think that $175 7424XP was a package deal with extra pads and whatnot, I just did a quick Google shopping search and saw it for $120.
But really if your paint isn't too bad right now, I'd really suggest you do it by hand until you save up the difference for a decent DA polisher. It's a tiny car, shouldn't take too long.
Also on time vs. pad size, if you are using a good-quality polisher with the right pad and compound for what you want to achieve, it doesn't take long because you aren't going back and forth over the same area much. You can get alot done with a 4"-6.5" pad. It is *nothing* like those junky 10" ones with a microfiber bonnet like they sell at auto parts stores and whatnot.