Hi,
First, I have no idea of value. Holland & Holland are premier London gun makers but this gun does not reflect their quality IMO. I suspect it was made for Abercrombie and Fitch to sell in their stores during the American Bicentennial in 1976. Perhaps that gives it some higher value, however, it is a lousy representation of a long land musket from the Rev War period. There are many things wrong, the lock markings, the side plate , the forward ramrod pipe, etc. This was meant to sell to folks who did not know better. I would want to look at the inside of the lock. If it was well made, I might pay $900 so I could work it over and turn it into something historically correct.
dave