Depends greatly on quality of the snow. I would suggest looking through the classifieds to know what they are going for... but typically they are going for 100-175. Although I recall seeing one go for like 60 from someone.
I hardly ever see Black Holes for sale. Regular Mack Eclipses are usually anywhere from $100-$300, so I would price the Black Holes at $150-$350. If it's older, you would go with the higher price. Young and unsexed would be the lower one.
I agree completely with Kristi on what the pricing should be. However, at all the shows I vended and attended I didn't see or sell any Black Holes for more than $225. Yes its a show and yes prices are usually lower...but people just are not wanting to fork out money on anything right now. The prices I said are what I observed them selling for. I know some of the bigger breeders have them listed for 350ish, but they can do that. I would certainly start higher (especially if they are older or have nice white and all) but you may have to drop prices to actually sell them.