No additional charges; everything is inclusive except the 'low pressure' sensors.... IF you need one or more.
You'll have to compare the tire prices on your own. A couple of phone calls and you should be set. You can't see the price of the tires, because different models and sizes have different prices. You must call both shops... and don't forget to ask 'the other' shop
if there are any installation costs to factor in.
Costco used to put in all new valves and stems... but I can't recall, now, if the stems are integral with the 'low pressure' sensors. It may be that some are.
PERSONALLY, I prefer a higher quality tire to those, generally, offered at discount houses.
hope that helps.
Thanks! I called both. Same tires ended up costing the same at Discount Tire vs. Costco. Little better Road Hazard at Costco. More money back with my AmEx. I'll be going with Costco, thanks for the advice.