OK Xbox Game Pass Ultimate pros. I want to get my son set up with 3 years for as cheap as possible.
Since your son still has that $1 offer, you'd probably be best to do the Cost Co 2 year offer, along with a ~$60 Gold Subscription card. Right now 3-Months at around $20-25 or more depending on tax makes a year of Game Pass higher than $60 for a year of Gold to Game Pass swap. The same is true with EA Pass' changing to 4 months of Game Pass. So your Cost Co option is keeping you under $180 for 3 years, which these sales likely aren't beating.
But, considering how aggressive Microsoft is being with the start of this generation, and that the holiday spending is just beginning, you might be better to wait and see how things progress in December. Maybe they'll have more sales on Game Pass as Christmas gets closer. Microsoft really seem to be pushing the value of that, and it seems like in prior years Black Friday sales were either repeated or even better with select retailers as the weeks moved in December.
And with how this year has been, it seems like some of these retailers absolutely will be fighting for revenue and need to have competitive pricing to grab consumers.
Basically, for your son nothing is beating the Gold to Game Pass conversion. Unless in December some serious offers come to the 6-Month or Year subscriptions to Game Pass, I don't think a first timer can beat the $1 conversion (especially for 3 years). But if you're doing this as a Christmas gift, it wouldn't hurt to wait and see if anything comes along that somehow (unlikely) beats your Gold to Game Pass option.
Also, your son might get that 1 month extension when redeeming a Gold card, which would cause a problem for trying to load 3 years before switching it to Game Pass. He might need to wait a month with Gold active before adding the remaining code (either the 1 year or 2 year left over code) and then redeeming the $1 offer..