Bending the types of radius bends you need for the roll bar hoop will take a special bender. Most Cobra roll bars use a 12" center to center radius roll bar hoop, which takes a hydraulic bender with special shoes. They are very expensive. But you can't get by any other way if you want your hoops to be strong and not have flattened pipe at the radius.
Most of the other pieces can be made with a Harbor frieght bender if you choose.
I had to do a lot of searching to find an outfit that would bend my hoops and finally found
www.peytonperformance.com in Texas and they bent my hoops and sent me all the pieces I needed for a very reasonable rate. I think I had around $300 in both my roll bars with the braces, tenon pieces, sleeves, and shipping. The hoops came out very nice and round without having to pay for mandrel bending, which is very expensive for small runs of bending as each size and radius requires a separate set of mandrels. My 1 3/4" x .134 pipe (SCCA requirement for sanctioned races) would have taken a special set of mandrels and bending shoes which I was quoted several places at around $12,000 dollars. To bend nice, round bends without flattening without a mandrel bender takes some considerable skill and lots of practice.
Hope I didn't take too much air out of your sails, but a bender can be a handy tool for lots of other things and they aren't real expensive. I used a cheap Harbor frieght unit to help me build some of my suspension pieces and body hoops.