How "little" are we talking? 58 isn't super low, my barn during the winter is usually around 55, just make sure that you have a house for him to go into and that will help him stay warm. If you have fleece hammocks or a bag, put that in there as well. You can also help by covering 3 sides of the cage.
Space heaters aren't very expensive. Check a Wal-Mart and see what's available in your area. It's always good to have a back up.