Harold Newton Original Oil Painting

Harold Newtown is often known as "the original Highwayman".  I've been able to read and learn a lot about this incredible artist and even saw that some of his paintings are a part of the Smithsonian's permanent collection, however I can't find too many of his pieces online for sale to really gather how much this may be worth. It's a rather large painting that was purchased directly from Harold while he was traveling selling his work. It has had one owner prior to coming into my possession and is still in the original frame it was purchased in.

I brought it in to a local art studio in the small town I live in and the owner told me it was worth at least $2,500 and he'd buy it from me right then and there - I thanked him and kindly declined as I feel honored to have come into possession of this painting but also felt that his eagerness to sell it to me for $2,500 was a sign that it was likely worth much more. 

Would love to hear some thoughts on this piece!