One, always go for a much higher rating than needed. As others stated, the rating is typically for pairs. Paying an extra $20 for much higher rated jacks is worth it if it has even a 0.001% chance of saving your life. Which is does.
Harbor Freight will work. I'd recommend better, but they'll work if you buy drastically over the rating you need. With any jack, try to inspect it carefully. And obviously be careful in placement. Do not, repeat, DO NOT, try to make your own. KD5NRH, not sure if trolling or just giving irresponsible advice. That's on par with shoving a fork into an electrical outlet. Short of very specialized applications like aircraft or crane support, you should never try to make your own jacks. Even the custom jacks we used for very large aircraft were commercially made or special ordered with the welds x-rayed for quality control. Unless you have professional welders of exceptional skill AND the facilities for non-destructive testing, that's not a bad idea, it's a dangerous one.
Buy commercial jacks, buy bigger than you'll need, spend the money on quality. Any brand name is fine. Even overrated Harbor Freight jacks are fine so long as you inspect and test before putting anyone under the vehicle. In a pinch or if you don't feel like doing that much work, go on Amazon and pick jacks with lots of ratings.
Torin T46002A Double Locking Jack Stands - 6 Ton, 1 pair are $57 on Amazon and I'd definitely buy a set if I didn't have a four six ton Craftsman jacks at home. The locking pins are nicer than the ones I have and I'm actually tempted to upgrade. I did buy one of those quasi racing style jacks from Harbor Freight. It lifts my truck for the jack stands, and I don't bet my life on it. I do actually recommend them, just not for safety critical applications.
