I'm interested. I like Hellboy a lot, but I'm not sure I would go $150 on a tooth fairy model (a kit at that).
I think something iconic and chunky like the Hellboy comic gun, can garner a $150 price tag as a kit. The tooth fairy which was a cool minor enemy in the 2nd movie, I think you will find harder to sell at that price point. I think at $100+ I would try to make my own out of clay or commission an action-figure artist to make one for me (one that articulates in positions. Maybe a closed and open mouth interchangable head).
Gentle Giant did a Tooth Fairy Maquette which was limited to 250 manufactured, and those are pretty darn rare, but they occasionally pop-up on ebay for around $250-$350. But those are a numbered, limited-edition, licensed, official pieces; that are assembled and painted with a base (finished display pieces) and box. I wouldn't even go that high, if the person didn't have the box.
On the other hand, upon seeing a really cool prototype, I could very well eat my words.
Honestly, I collect the comic books even though I'm a fan of the Guillermo Del Toro movies, I'd probably be more interested in a comic book /MIgnola version. But I'll be watching with interest.
-Terry