Have you checked the Blue Book of Gun Values? It should give you an idea of the values in the USA. Of course the value of a gun in Canada can be much different from the USA.
Your first gun with the 4" barrel will have a limited amount of buys that can buy it due to it being a prohib due to barrel length. Have you checked to see that it really is a 4" and not maybe 4.13" or more? Can't hurt to check.
How about posting some pictures?
Fudd