Oceanic/Aeris Accel fins are pretty buoyant.
and they can be had for $60.-
Oceanic Accel Adjustable Strap Fins
(Yeah, I know, not everyone's favorite store, but a good price)
and they have posts onto which spring straps could fit (but then they would be heavier again)
and they could fit (just) into right sized (maybe soft, not hard, I use a backpack) carry on luggage
yes, they are not heavy duty tech fins, but they seem to do a reasonable job...