It also depends on what kind of tubing you are going to bend. A mild steel might work in the simpler tools. But a strong hard steel or chromemoly tube cant be bent without a mandrel.
Check out http://www.mittlerbros.com/. Alot of the race teams that build their own chassis use Mitler or Irwin-Smith. I have used Mitler notchers and bender. They are super nice.
Speedway motors sells a super low dollar bender. Bender & 1 set of dies 399.99. Or complete set of dies & bender for 799.99 check them out at Speedway motors.com.I use pro tools one shot bender & mittler bros. notcher.