Yaris will work...but if you have to put on different winter tires and chains and what not, obviously its going to effect handling and fuel economy, so you might be getting in the upper 20's low 30's for mpg but I guess anything is better than 18mpg. I'm NOT saying the Yaris is a bad car and can't handle snow, but in your situation, maybe something different...like a 4wd Matrix? But if you have your heart set on it, go for Yaris...or as stuts suggested go for a compact truck-not Ford (sorry stuts), you'd be lucky you make it a year without problems-okay I'm a little bias

Good luck and hope all works out! Keep us posted!