I really don't think $29k is too much to ask. The fact that this is the only one ever made, and ever will be made is a whole lot of value in itself. Solid platinum, add another $5000 to the cost. The fact that this is a real collector's item; something LEGO doesn't do often is again, an extra few thousand dollars.
On a side note, before selling something like this, surely he got it appraised. Whoever appraised it would have experience in marking the value in these things, so the price is certainly realistic from a collector's standpoint.
As they say, something is just as valuable as a madman wishes to pay for it.
But yeah, without the emotional value it would be worth about $7000. The fact that there was only one ever made, and that it's an ultra-rare collectors item many would dearly like to see on their own shelf (or safe, for that matter), enables him to ask whatever he wants for it: we can't get a cheaper one from wherever, and there'll surely be one collector rich enough to buy it.
If it doesn't get sold at this price, though, he'll probably try again asking for a lower price later.
Makes me wonder, what if someone were to create a mold of a regular Avohkii, fill that with platinum and then resell it? The actual item is so rare, we wouldn't have enough material to compare it with to determine whether it's a fake.