I've brought a few pins back from Canada to the States.
Rarely questioned going INTO Canada about why I was going to get a pin.
On the way back, questioned heavily (as the US customs can be pricks) about the pin. One time I even got a car search performed with a wh20 in the back. (cringed thinking they'd rip thru the pin). But never really asked about price, etc.
Just play up the collector aspect of it. I think 95% of the time you should be fine.