Look at the prices for things such as front floor mats, frunk/trunk trays and (if interested) a car cover. I was able to do much better on pricing for those items by buying GM OEM from an online GM wholesaler (in this case: BuyKippScottGMParts.ca in Alberta, but they will ship to you in Ontario, if you don't find someone else local) rather than putting them on my order for the car or buying them from my dealer. I didn't install the other "bigger ticket" items you've mentioned but know others who did and they paid ++ getting them from the States, given the US exchange rate and ship charges...plus they also paid for installation which is usually included if you buy direct from factory as part of your original order. Best to check on whether install comes included with the price, if you buy from factory or the dealer.
Sometimes some items aren't available direct from GM, so some of my friends were happy to pay more just to get them. That may have changed now but you're likely better off researching what you want and comparing it to what's available direct from GM. Then on top of that, you may prefer what the aftermarket is able to offer, compared to GM OEM. For example, I didn't like any of the OEM rims so purchased new ones from MRR Wheels in Los Angeles (a Forum sponsor). Finally, I've been able to negotiate discounts on accessories with dealers I'm buying a car from, in the past with other vehicles. Maybe with this being the third year for the C8 you'll be able to do that with your dealer? Hope this helps and I invite others who've purchased the "body add-ons", to chime in.
