I did a little research a while back and found out that you really need a bender that has dies that support both sides of the pipe to get good quality repeatable bends. This is the cheapest ready made unit I found
Model 3 tubing bender by JD2
at about 300 bucks for the manual bender plus anywhere from 115 to 300 dollars for a set of dies for one size pipe. The price varies depending on the minimum thickness and what radius you want. If you do a search for "diy tubing bender" you will find people who have made their own with purchased dies and even some who have made dies from pulleys and such.