Bands: I would start here. For less than $30 you can do a full workout routine. You won't get Phil Heath big but you will get started.
Don't take my word for it. Check out the Muscle and Fitness 4-Week Strength Band Challenge.
Doorway Pull Up Bar: This is the next thing I would get if on a budget. Besides pull ups you can use it for push ups and tricep dips.
Dumbbells: You can get alot done with just dumbbells. This is another good place to start for a low price. Get star locks and add weight as you go.
Barbell Set: A barbell and a imagination are all you need for a complete workout.
Bench: This is the next logical step.
Power Cage or Squat Rack: Now you are in the big league.
