Without further information and/or examining the weapon it would be very difficult to say. Rarity and condition of course being the key. This one is not exceedingly rare, and is not in mint condition and appears to have missing parts....

An Artifact's book "value" has been frequently running much different than what its "market value" may be. The economy has depressed the sale prices of many things including civil war artifacts. People finding decreased values, and or finding tough times habitually will try to offload such extras first. In many areas the market is flooded as a result which has only further drops the prices. Buyers tend to be looking for better condition, or more rare items at a good price, lesser ones going for much less. What value it may hold also can be found to be wide ranged, depending on the region. If it was in great condition Ive seen these in the past routinely go for around $1100-$1400 or so, again this will also depending on where and what the fluxuating market is holding at the time. In last two years Ive seen them go for anything around $400-$900, depending on condition and any documented historical provenance. Majority that Ive seen typically are in the $500-$700 range lately. Some sold, many dont... If it has issues then much less... others milege may vary.
Just an opinion and observation...

Frederick