Use a bubble mailer with cardboard backing and send it registered...its around $14 from anywhere in Canada to anywhere in Canada.
But if you didn't specify that if an order goes above a certain threshold (say $50) that it would require shipping with tracking you shouldn't require it and you should send it all for $4 regular mail or cancel his orders or pay for the registered mail option (that I detailed above) yourself. I would to the last option personally.
As a seller you should ALWAYS list combined shipping details in your ads and require payment for tracked shipping if an order value limit has been exceeded.
