But its more fun to shoot off the mouth/keyboard here..
Interesting thread but seriously, it is not possible to make a strobe for $20. Electronics is one thing, but water proofing to 150' is a totally different thing altogether. We can argue about how much the components cost till the cows come home but hey, that can be said about almost ALL electronic products. Ever wondered why a Nikon SB800 cost almost US$300? So if a surface strobe costs US$300, which should a underwater one cost less?
In any case, because of the small size of demand, there is no mass production of these strobes which also increases the cost. Not to mention the man-hour cost, the intellectual rights cost etc etc...
At the end of the day, if you don't think its worth to pay US$500 for an Inon, don't.