I believe it's 50c/min on the current plans but it depends on when you got your plan. Or maybe you don't have service with Koodo yet.
It doesn't cost anything extra to receive calls from the US, though. It just uses airtime.
If you want, there's a $10 add-on for unlimited US long distance. But it will still use airtime. So let's say you have a plan with 200 Canada wide minutes and the US add-on. If you call the US it will still use those minutes. If you run out of minutes and want to call the US, you won't pay any extra LD fees, but you will be charged airtime overage.