I think winter tires are completely worth it, especially on a Subaru. But, you don't have to buy new ones, look on Craigslist. I found 4 General Altimax Artics with one season on them for $180. Just look around. Honestly, best winter tires I've ever used.
Be careful doing this. Most snow tires have a base rubber compound that's hard as a rock. The soft rubber only goes down to about 50% tread life. Most snow tires are shot at 50%. There's a reason why you see a bunch of 50% worn snow tires on CraigsList and the like.