I've been watching an upward trend on these for a few years. Dealers seem to be generally pricing in the $500-$700 range. Auctions might yield a bit less than the lower price. There is a clamor for scabbards, so swords with scabbards are selling at somewhat of a premium. There may be a cache or three yet to be uncovered but if you have to have them, price is a bit relative anyway.
One note is to be careful of reproductions. The Windlass is easy to spot, no markings and the weight difference is substantial. The swords from Sarco Inc. bear watching though. They are marked, the shape of the bowl and grip is better than the Windlass and the weight is much closer. It is worth looking closely at their pictures (no link handy)
There are some web pages dedicated to the sword which explain correct marks. Google for those and dealer listings and you will see a bunch of info and examples.
Go for it, if they seem right to you.
Cheers
GC