I would second Dave (of who's posts I'm quickly becoming a fan of). I haven't done such mesurements but from experience I would claim the following.
Far more important than material or price is the correct fit and stiffness - this goes for mono's as well as bi fins.
Fins may well "feel" different, but as far as actual performance, at least for me, pretty much any decent fin will get pretty close to the same result. The differences are really marginal compared to for example correcting your technique by choosing a correct stiffness or being able to wear your fin for more than 5 minutes without agony.
With cheaper fins you have the freedom of trying out more combinations of stiffness/fit. It's pretty much impossible to say what's the idal combo, because it is completely individual and what's more, keeps changing with your experience level. So better try a few combos for a while (trying a pair once or twice doesn't really tell anything).Once you find yours, then maybe buy those $500 fins...? Generally for beginners it is safer to start with too soft rather than too hard. Even though the opposite seems to be what beginners usually think (Better get "stiff enough" so I don't run out of power!")
My next bi-fins will be made of plastic and relatively soft. Mainly because I would use them for (non-competitive) spearing, recreational freediving or photography, so I don't need every % of performance, at least as a compromise to comfort in long surface swims and long sessions and the fact that I don't have to worry about hitting a few rocks or splitting the fin with a sideways motion...If the purpose was competitive dynamics or CW with bi-fins at world class level, it'd of course be a little different - but not much.
