The Green River Rifle Works in Roosevelt, Utah built copies of Hawkens, Lemans and Poor Boy rifles in the 1970's. Not replicas, but copies of original rifles, quite faithful to original rifles. I built a Leman in their shop in 1978. My friend Neill Fields started there making barrels and went on to build rifles. He has now built over 400 muzzleloading firearms. I just phoned him about your request for info. He said the Hawkens sold in 1978 for about $500. We would know the name of the builder if there is a name on your rifle.
If you buy the parts from Track of the Wolf to build a Bridger Hawken, my catalog shows $661.59 for parts, using a plain maple stock. Neill got $5 per hour back then, he gets $40 an hour now. He'll build you a Hawken for about $2500, depending on quality of wood and barrel. There may be a collector's premium for a GRRW Hawken, I don't know. But just looking at it as a good copy of a Hawken rifle with premium parts, do you think it is worth what the asking price is?