I think that is very cheap for an all correct original (non India Pattern) Brown Bess, although I'm not that familiar with market values for these nowadays ..
For comparison...
Here is a 53 pic photo montage of my own 1808 Brown Bess Tower Musket - India Pattern (click here).
It's all correct and all original parts (no repros). I've owned it for over 40 years …
(Click PIC to Enlarge)
Note that it also has the early cocking piece (not a full closed throat) like the one you're looking at...
You might want to try our Google CSE custom search engine located in the top right corner of the web site titled Search Milsurps.Com. It only searches our site using Google techniques and can be quite fast and more efficient then what other gun sites on the Internet utilize. For example, in your case, type in the words brown bess and see what happens. There are dozens of old threads with many with pictures that you might enjoy, covering various aspects of this topic.
Regards,
Doug