The seller said the light blue Kakama sold for $4,500 but I know in auctions like this, the higher bidders very often fall through and the sellers contact the next highest bidder(s). I think @Darknut probably has more info on this specific auction. I was expecting that one to land in the mid $2,000s and I think that $4,500 surprised everyone. My guess is it went so high because the seller has a good reputation, it was a cool color, and because a couple of the die hard fans who are actually willing to shell out that much money happened to know about the auction and have the cash/credit available.
@Owls I speculate the rank in "value" of your prototypes would be
1. Dark Turquoise Matatu (Because Dark Turquoise is really cool and because it would color match Kongu)
2. Yellow Ruru (Because of the Sand Tarakava Hype, but not #1, because there are at least 3x others of these out there)
3. Sand Green Rau (Because Tamaru and sand green is cool)
4. Violet Huna (Would rank 1+ higher if it was in a cool shade more commonly used in Bionicle)
5. Dark Orange Mahiki (Even though this is a color match for Huki, #5 Because kanohi in colors related to Po-Koro tend to sell for less (with the Trans-orange Kaukau being the exception), and the Mahiki is one of the weaker noble mask designs) The Brown Komaus go for much less than the white and yellow Hunas. (I know it is more common, but the color does play into it more than people realize)
6. Light Blue Trident (Because it's not a kanohi)
I speculate at the upper end of the rankings you will find a couple people who are willing to pay close to ~$3,000-$4,000, and at the lower end you are looking at ~$500-$600. A lot of that depends on the perception of the parts being genuine and your reputation as a seller.