Black candles are essential for ritual. Personally, I prefer tapers because they cast the light better than pillars. But it seems to me that black taper candles are becoming harder to find in retail stores. I used to see them frequently enough but now, not so much.
The best on-line deal I have found is at http://www.generalwax.com/
There I can get a dozen 10" black tapers for $9.69. There are even cheaper if you order a case of 144.
I previously ordered a dozen of the same candle from Candles4less.com. I paid $12.69 (plus $6.59 shipping) only to notice on the label that the candles were actually made by the General Wax company linked above. So, not shocking, its cheaper to buy them from the original maker.
Consider yourself educated.