If it is their original version of the Hawken in flintlock it would be worth somewhere between $250 and $400. I used one of the locks to build a ML shotgun about 30 years ago and it worked pretty well. It doesn't spark as well as many of the more traditional locks put out by people like Siler and others but if you keep your flint knapped (sharp)it will work o.k. BTW, don't fill the pan with powder (do use FFFFg), rather put in about half a pan full and bank it toward the outside of the pan so it will "shoot" the flame into the touchhole, you'll get faster ignition. It will work best with real black powder as Pyrodex and Triple Seven are harder to ignite. I have used pyrodex but put a small bit of black (FFF or FFFFg) down the tube first as a kicker for the pyro.
Follow through on the shot.
Best luck, Stan
(I bought an unfired Hawken percussion version, made in the early 70's last year for $250 at a gun shop....people, unfortunately, don't want traditional guns, just the inlines. Good for you for wanting to give it a try.)