Thats an old one. I don't think it is a Grummley, but if it is the value is high...really high. In any case, ifthey are asking a reasonable price for it, you should jump on it.
This could be one of thase rare occasions when you stumble upon a realy find.
It is an old brush bow, say early '50's, but it will take someone more knowledgeable than me to put a real year ID and value on it.