Where is the best place to buy tires, and which brands/models would you recommend?

I desperately need new tires for my 2001 Chrysler Town & Country minivan, but am not sure where to get them, or what type I should be looking for. We get plenty of winter weather here, and I do a lot of highway driving. I need decent tires that can handle those conditions but I am brokety-broke-broke, so cost is a HUGE factor.

I have never bought tires myself before, so any advice you can give me will be greatly appreciated. Thanks!