As people said, make sure you can afford the insurance first.
Second, RWD in the winter is not a problem as long as you have a full set of proper winter tires. Actually winter tires are a must regardless of the driving wheels. RWD, FWD, AWD, 4WD, whatever -> get proper winter tires for winter driving.
Now, there are also plenty of other choices that are more fun than a Tercel and won't cost as much to insure as a Mustang. Mazda 3, Mini, Civic Si, Impreza, maybe Impreza WRX, heck even a Miata; all of them are fun to drive in their own way and would be an upgrade from the Tercel.