Depends on the furnace, Blackburn, and how much associated work is required with it.
Your best bet? Get a bunch of quotes, but make sure that they all quote to the same specifications.
The soapstone stoves are nice, but they're not cheap at all.
CFABE,
Be sure to include the cost of a chimney liner or stove stack in your estimate. Many areas require that, if you vent a freestanding woodstove into a chimney flue, that you line it with a smaller diameter pipe. This can add several hundred dollars to the overall cost.
Even if your zoning requirements don't call for this step, it is an EXTREMELY prudent thing to do.