I would definitely recommend looking for a set of steelies with snow tires on them already if you have a place to store them in the off season.
Used tires will last you a while if you are swapping them on and off.
Also, in your search for a set or if you decide to buy new, if the car is front wheel drive, you really only need 2 wheels and tires. Other then looking funny if the car doesn't have steel wheels and hub caps in the front, most of the traction needed (accelerating, braking and turning) is done with the front wheels. And if you already survived a winter with regular tires, front only snow tires will for sure to the trick!
Also, added benefit, the 2 tires tread wear will not last as long because you can't rotate them front to back (the snow tires i had were directional so you couldn't do the star pattern or just side to side) so they will need to be replaced eventually, but since they sit so long in the other season, the rubber will most likely dry rot before the tread is gone anyways. The soft flexible properties of snow tires is what really allows them to have good grip and keep snow from getting stuck in the tread. So you can get a second set of front snow tires some years down the road, when all 4 would have experienced dry rot at the same time.
edit:Agreed with the comments below, sorry for poor advice and not really thinking about it in a commuting sense, highways and on/off ramps with hard turns at any speed or swerving is not a good receipt with limited traction in the back.