You cannot beat the cost of promo ammo from Cabela's or the like, if you have to pay shipping. Shipping ammo is expensive in Canada.
Despite what is said by poster above, four flats of shotshells (1000 rounds) is a trivial amount and you cannot expect a significant discount on that amount.
You can get a good price on shotshells if you are buying pallet lots from Challenger or Score. Many clubs do so, setting up a bulk order, as a service to their members. Challenger or Score offer good prices because they are competitively priced in Canadian Dollars.
US manufactured Promo ammunition priced in US dollars cannot come in at less than $65-$70 a flat plus taxes - check out what our puny Canadian dollar is worth these days. Needless to say, quality competition ammunition costs more. We do not have the deep discounters or Walmart prices for ammo in Canada, but our prices are pretty good, when you shop the best sales and stock up.