Just be careful of the Joe-schmoe that has a tube bender and a welder in his garage and offers to build the roll cage for 1/2 or 1/3 the price.
Roll cages, especially in race vehicles, need to built by someone that really knows what they are doing with the tube work, notching and welding. They need to understand how to engineer a cage that will hold up in a wreck. Remember, this quite possibly could save your life when things get out of hand, is it worth saving $500 on a roll cage only to loose your life due to a poorly built cage?
I'm a Joe-schmoe with a welder in my garage and a tube bender... when it came to my TJ build, I opted to pay the price and had Ben Hanks Racing build my cage. It was much safer than what I could have done and I felt good knowing that it would hold up to some serious abuse. Sometimes you just have to buck-up and pay the price for quality.
I'd recommend any of the well-known fab shops that advertise on here.