Lee Valley is the absolute best prices I have seen in Canada. They get them straight from Dan's and the Hard Black at Lee Valley is the same stone as the Black Hard from Dan's website which is their finest stones. At $104.00 Cdn for a 8" x 2" x 1/2" Black Hard Ark you really can't go wrong.
When available, Dan's will sell "end cuts" , one flat face and what is left after a block has been cut in slabs. You may have to use it hand held instead of on your bench but you can get a lot of Arkansas real estate for a good price. Email or call and they'll send pics and price of any available at the time.