A seller on BrickLink has listed a Prototype Sand Tarakava! I have no idea if it is authentic, but I have passed a message to Mark of MoD in case he would be able to verify its authenticity for us. Listed for $225.00 USD, it may seem a bit pricy, but the cost is actually reasonable for a collectible like this. Even if it’s outside your budget, this listing gives the community a higher resolution photo of the model, and seems to answer a question or two about the parts comprising it!

The seller also provides this information about the model:

I acquired this set from a lifelong collector when I bought his collections. The mask is an orange Ruru. The jaw is black- I have seen some imitations use flat silver, but this is incorrect.

I know some readers will appreciate that information, given that the exact color of its jaws have been the subject of a debate or two in the community.

UPDATE: The listing has apparently been delisted, deleted, or sold. If I understand correctly, it may not have been an authentic Sand Tarakava prototype according to information from Mark. While it was delisted before he could get a look at it, he provided this information:

The mask is the easiest tell. You’d have to have a yellow Ruru prototype mask from either a Sand Tarakava or the pre-release Manas. IIRC, several other parts were also prototypes, but they require closer inspection. The other hard-to-find part would be the tread. If the treads match the regular Tarakava, it’s not a 100% legit Sand Tarakava.

However, TuragaNuva on the Mask of Destiny Discord had this to say about the listing:

The guy that runs that BrickLink store is pretty established and knows his BIONICLE. If he claims that’s what it is then I’m inclined to believe him.