You're right about the fact that we pay stupid fees to import stuff from the US.
One solution is to find a seller that accepts to ship USPS (post office). The packages are transfered to Canada Post, and the fee to clear customs is a flat rate, like $7. UPS and FedEx and others, charge a percentage which is a big chunk of money.
Another solution, (I do that once per summer), for stuff that is not an emergency, I put everything I need on a list, then I have everything shipped to a warehouse the other side of the border, and offer the wife/familly to go for a drive, in the states, take a beer or sangria on a terrace, and pick up my stuff coming back home
Often US sellers offer free shipping within US and when the parts are made in US, Canada, Mexico, there is no duty to pay, only the sale taxes.
For the front flares, check with the dealer for the LeMan kit (4 flares). If you are a member of a BMW club, you will have a discount. The price is not that high. Take a look just in case.