Those are a lot cheaper than I expected them to be

Swiwin makes even cheaper, more powerful ones. 6000$ retail for a 400N jet. Though, it is a Chinese company, so I would test the engines pretty carefully and a carry a parachute just in case.

The trouble with jetpacks is that there is a large dead zone in the flight envelope. Too high to survive a crash but too low for a parachute to be effective.

Very true, but to be fair with four engines and a wing you'd need 3 engines to fail out of four to be in a catastrophic situation.