Not too sure what size wheels are on the car to start out with, but I would not put on a larger size wheel for the winter. Larger tires are going to cost more, especially for winter tires.
For a decent set of winter tires, you are going to pay a good amount. Depending on tire/size/etc, you’re looking at spending probably $400-550 for tires alone. I got my winter tires from Discount Tire Direct and they were $120 per tire. This was the first time I had ever used true snow tires and it made one hell of a difference with my car so it was worth every penny.
I happened to pick up an extra set of OEM wheels for cheap so I could use them just for the winter wheels.
If you’re looking for new wheels/tires, are you planning on getting a set of winter wheels as well? Perhaps you could buy a nice set of summer wheels and tires, then use the stock wheels for the winter. If you don’t want to go this route, you can check on Mazda forum’s for people selling their stock wheels. Most of the time you can pick up a set really cheap that are in good condition.
I actually want to get some winter rims to keep the stock ones nice. I have one of the higher trim levels and the wheels are 17"s and are pretty nice and I want to keep them that way. I really don’t care what size i get for the winter wheels as long as they are cheap. Maybe I can find some on ebay or something.