TireTrends.com price is $161.70 for P225/55/17. If they are only charging you $75 per tire for the switch, they're doing you a favour. They probably have customers (who don't know better) commonly ask for replacement RE92s.
You will not get a lot of positive comments about the RE92 from driving enthusiasts like those on this forum, but they should be fine for your trips to Ottawa, especially on the AWD Subaru.
To me, it's a wash. The dealer is not gouging you on the swap. He is making some money, but I was afraid in the other thread, that he would charge you $120/tire for the swap. At $75/tire, it might make sense for you.
Economically, of course, you're probably better off keeping the RE92s, even if you change them well short of the wear bars.
And I know the rain you speak of on the 401 to Ottawa. It can be nasty.