I understand the need to bring something. I nice bouquet of flowers is always a safe choice and can fit a wide variety of budgets. Chocolates are another good choice, as is a homemade dessert that is wrapped, as you say, as a gift not an eat this now type if thing.
If you choose to bring wine, many wine shops, and even Costco, has cards telling about the wines, frequently including point ratings. In my experience, I'd say that <80 points usually is not a good thing, 80-85, okay, 85-90 is good and over 90 is very good. As you approach 100, the price often goes up exponentially. I'd try to find something around 90 in your price range, which should be doable if you can spend around $20. I've never seen a rating on a card under 75, and even 80 is rare.
Since they are going considerably out of their way and it's the holiday season, I'd err on the side of getting something that's a bit too much, perhaps a bigger box of chocolates or something like that than you ordinarily would.