I'll give you my two cents based on limited experience.
What's your other vehicle? Is this going to be your primary ski car?
To my knowledge there's no AWD version of the Civic, Elantra or Sonata. The Subie only comes in AWD, so it's not really a fair comparo. AWD = better traction, worse mileage. You can squeeze 42+ out of the Civic and I'd be surprised if the Subaru got much over 32. PDQ would know what kind of mileage you can squeeze out of an Outback, which should be comparable.
We've got a 2006 Civic, but because we've also got a CRV, we've never driven it in the snow. I'm betting it wouldn't be very good. Ours is a stick, and even on dry pavement it's not hard to spin the tires. It's odd because it's not really powerful.
Hyundai is looking like the next Honda - really good quality cars and great price. Cool styling on some of them too. But no AWD on the small sedans.
If it's going to be your primary ski car, I'd go with the Subie. We've got a really steep driveway in the mountains and the Subies our friends have, blow away our CRV on that hill. (We went with the CRV for the cargo space.)
"You just need to go at that shit wide open, hang on, and own it." —Camp
I drive a Subie Forester and put some snow tires on it for the winter. It's unstoppable in the snow...It's our first Subaru, and we've decided that from now on, one of our cars will always be a Subaru...
I also owned a Civic a few years ago and it handled Buffalo winters just fine. When I was home from college for winter breaks, I used to do commercial plowing. That meant I had to drive to the shop to pick up the truck, most often before the city/town plows had a chance to clean the roads. The Civic did very well, even when we had 81 inches in 5 days, like in December 2001.
It's all about the rubber on the car and the person behind the wheel....but AWD sure is nice...
Take a look at used Audi a4 4cyl turbo. The 2006-2007 are coming off lease and might be in your price range. I had a 2004 and I got 31-35 on the highway. Mine was a 6 speed man. The engine and drive train are bullet proof. At least test drive one even if you do not think it is for you. It is a joy to drive.
What is more important: (a) getting to the slopes in good time and in one piece, or (b) saving a little money on gas? If your answer is (a) buy the Subaru. We have a 2009 Impreza Sport (spent a little extra to get the heated seats and sunroof). Mileage is OK, the car is super-fun to drive and as others have said, it is unstoppable in snow (unless it is very deep - somewhat low ground clearance). I put four Hakkapeliitta R snow tires on it and have never felt as safe in any vehicle. This car is my third Subaru. Last one was a '96 Legacy wagon, which we put 375,000 km on. Where we live, there is a lot of winter driving and all our vehicles are four-wheel drive: Subaru, 2003 Toyota Tacoma, 1985 Kubota tractor.
When Subie-shopping, I did entertain the used Audi idea. Then I read the reliability reports. Not so great, despite what others report in this thread.