Sickle is not a very strong keyword. A check of overture keywords shows that most searches for the term involve sickle cell anemia (a disease) or the Hammer and Sickle (symbol of the communist party). Neither of these things have anything to do with business. Also, .biz has very low value compared with the older gTLDs.
The only business having to do with the term seems to be Sickle Climbing, and they already own Sickle.com. So you won't be selling it to them.
IMHO I'm going to say reg. fee... sorry.