We're a rich kid in a high-risk high-reward job and various npcs frequently mention needing to save up for their transformatives or to pay off debts. Both price points a typically a couple grand a pop. Again the cuffs don't seem to be all that powerful and probably can't move all that fast while holding onto a person, which they probably manage to do mostly by having the person's limbs bound in a position where they can't get leverage.
laws, safety, again power efficiency.
Also the jetpack is a device that is engineered to jetpack around and is not only 10x the cost of a pair of grav cuffs, but is likely far larger depending on the exact model you headcanon it as having.
Bah. It's 10x the cost because it's a piece of equipment instead of a sex toy. You see the weapons on Myrellion? 3-5,000 credits for an old-timey bolt-action rifle or shotgun. 2-4,000 for an axe or sword. 6,000 for a freakin' flare gun! 8,000 for a bow! The prices of equipment is arbitrarily inflated because money sink.